Greetings our team recently merged a few records, and in some custom objects, we seem to be encountering some faulty flow errors, as evidenced in the debug log.
 

39.0 APEX_CODE,ERROR;APEX_PROFILING,INFO;CALLOUT,FINEST;DB,INFO;SYSTEM,DEBUG;VALIDATION,INFO;VISUALFORCE,FINER;WAVE,ERROR;WORKFLOW,ERROR
21:54:17.0 (83548)|USER_INFO|[EXTERNAL]|005XXXXXXXXX|XXXXXXXXX@XXXXX.com|Pacific Standard Time|GMT-07:00
21:54:17.0 (154735)|EXECUTION_STARTED
21:54:17.0 (161449)|CODE_UNIT_STARTED|[EXTERNAL]|Workflow:01IA0000002K1qz
21:54:17.107 (107801764)|CODE_UNIT_STARTED|[EXTERNAL]|Workflow:01IA0000002K1qz
21:54:17.308 (308389351)|FLOW_ELEMENT_ERROR|The flow tried to update these records: a0l1200000AJIt2AAH. This error occurred: ALL_OR_NONE_OPERATION_ROLLED_BACK: Record rolled back because not all records were valid and the request was using AllOrNone header. For details, see <a href='https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_calls_concepts_core_data_objects.htm#'>API Exceptions</a>.|FlowRecordUpdate|Update_Member_School_Services
21:54:17.308 (368304171)|FLOW_ELEMENT_ERROR|An error occurred when executing a flow interview.
|FlowActionCall|myRule_1_A1
21:54:17.107 (387298617)|WF_FLOW_ACTION_ERROR|09L12000000Cc3M|30012000000LKtq|Error executing flow: Sync_Member_School_Service_and_School_Term, FlowDefId: 30012000000LKtq, FlowVersionId: 30112000000LAS7
21:54:17.107 (387319418)|WF_FLOW_ACTION_ERROR_DETAIL|<b>An unhandled fault has occurred in this flow</b><br>An unhandled fault has occurred while processing the flow.  Please contact your system administrator for more information.
21:54:17.107 (387413983)|CODE_UNIT_FINISHED|Workflow:01IA0000002K1qz
21:54:17.390 (390262240)|FLOW_ELEMENT_ERROR|The flow tried to update these records: null. This error occurred: CANNOT_EXECUTE_FLOW_TRIGGER: The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30112000000LAS7. Flow error messages: <b>An unhandled fault has occurred in this flow</b><br>An unhandled fault has occurred while processing the flow.  Please contact your system administrator for more information.  Contact your administrator for help.. For details, see <a href='https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_calls_concepts_core_data_objects.htm#'>API Exceptions</a>.|FlowRecordUpdate|Update_Member_School_Services
21:54:17.390 (410086409)|FLOW_ELEMENT_ERROR|An error occurred when executing a flow interview.
|FlowActionCall|myRule_1_A1
21:54:17.0 (428347702)|WF_FLOW_ACTION_ERROR|09L12000000Cc3M|30012000000LKtq|Error executing flow: Sync_Member_School_Service_and_School_Term, FlowDefId: 30012000000LKtq, FlowVersionId: 30112000000LAS7
21:54:17.0 (428369343)|WF_FLOW_ACTION_ERROR_DETAIL|<b>An unhandled fault has occurred in this flow</b><br>An unhandled fault has occurred while processing the flow.  Please contact your system administrator for more information.
21:54:17.0 (428470994)|CODE_UNIT_FINISHED|Workflow:01IA0000002K1qz
21:54:17.0 (429415510)|EXECUTION_FINISHED

Here's what the flow interview looks like.
 

Error element Update_Member_School_Services (FlowRecordUpdate).
The flow tried to update these records: null. This error occurred: CANNOT_EXECUTE_FLOW_TRIGGER: The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30112000000LAS7. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.. For details, see API Exceptions.
This report lists the elements that the flow interview executed. The report is a beta feature.
We welcome your feedback on IdeaExchange.
Flow Details
Flow Name: Delete_Member_School_Service_Or_Term_Sync
Type: Flow
Version: 9
Status: Active
Flow Interview Details
Interview Label: Delete Member School Service Or Term Sync 2/16/2017 10:43 AM
Current User: 
Start time: 2/16/2017 10:43 AM
Duration: 4 seconds
How the Interview Started
started the flow interview.
Some of this flow's variables were set when the interview started.
DeleteMemberSchoolServiceId = a0l12000005NmudAAC
DECISION: CheckVariables
Executed this outcome: MemberSchoolServiceIdIsNotNull
Outcome conditions: and
1. {!DeleteMemberSchoolServiceId} (a0l12000005NmudAAC) Does not equal null
Logic: All conditions must be true (AND)
SCREEN: Confirm_Delete_Member
Display Text: ConfirmDeleteMessage
Value at run time: Are you sure you want to delete this Record? This will resync the At Depth field across Member School Services and the Member Names field on the School Term

Selected Navigation Button: NEXT
RECORD QUERY: LookupMemberSchoolService
Find one Member_School_Service_Term__c record where:
Id Equals {!DeleteMemberSchoolServiceId} (a0l12000005NmudAAC)
Result
Successfully found record.
{!MemberSchoolServiceToDelete.Id} = a0l12000005NmudAAC
{!MemberSchoolServiceToDelete.School_Served__c} = 0011200001K6042AAB
{!MemberSchoolServiceToDelete.Term__c} = 2016-2017
FAST LOOKUP: FindSchoolTermForFlowFromMember
Find all School_Term__c records where:
Term__c Equals {!MemberSchoolServiceToDelete.Term__c} (2016-2017)
School__c Equals {!MemberSchoolServiceToDelete.School_Served__c} (0011200001K6042AAB)
Assign those records to {!SchoolTermForFlow}.
Save these field values in the variable: Id
Result
Successfully found records.
FAST DELETE: DeleteMemberSchoolService
Delete Member_School_Service_Term__c records whose IDs are stored in {!MemberSchoolServiceToDelete}.
Variable Values
[Id=a0l12000005NmudAAC,School_Served__c=0011200001K6042AAB,Term__c=2016-2017]
Result
All records whose IDs are in {!MemberSchoolServiceToDelete} are ready to be deleted when the next Screen or Wait element is executed or when the interview finishes.
DECISION: CheckTerm
Executed this outcome: TermIsNotNull
Outcome conditions: and
1. {!SchoolTermForFlow} (a0m12000001kyO1AAI) Is null false
Logic: All conditions must be true (AND)
SUBFLOW: Run_Flow
Enter flow Sync_School_Term_and_Member_School_Service version 24.
Inputs:
SchoolTermId = {!SchoolTermForFlow.Id} (a0m12000001kyO1AAI)
DECISION: Check_Variables
Executed this outcome: SchoolTermIDIsNotNull
Outcome conditions: and
1. {!SchoolTermId} (a0m12000001kyO1AAI) Does not equal null
Logic: All conditions must be true (AND)
RECORD QUERY: Lookup_School_Term_From_ID
Find one School_Term__c record where:
Id Equals {!SchoolTermId} (a0m12000001kyO1AAI)
Result
Successfully found record.
{!SchoolTerm.At_Depth__c} = true
{!SchoolTerm.Id} = a0m12000001kyO1AAI
{!SchoolTerm.School__c} = 0011200001K6042AAB
{!SchoolTerm.Service_Member_Names__c} = Allison Villa, Paige Tester
{!SchoolTerm.Term__c} = 2016-2017
FAST LOOKUP: Find_Other_Member_School_Services
Find all Member_School_Service_Term__c records where:
Term__c Equals {!SchoolTerm.Term__c} (2016-2017)
School_Served__c Equals {!SchoolTerm.School__c} (0011200001K6042AAB)
Assign those records to {!MemberSchoolServices}.
Save these field values in the variable: Member_Term__c, School_Served__c, Term__c, At_Depth__c, Service_Member_Name__c, Id
Result
Successfully found records.
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 0
Current value of {!MemberSchoolService}: a0l12000005NmuiAAC
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 1
Current value of {!MemberSchoolService}: a0l12000005NmunAAC
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 2
Current value of {!MemberSchoolService}: a0l12000005NmusAAC
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa, Paige Tester"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 3
Current value of {!MemberSchoolService}: a0l12000005NmuxAAC
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa, Paige Tester, Allison Villa"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 4
Current value of {!MemberSchoolService}: a0l12000005Nmv2AAC
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa, Paige Tester, Allison Villa, Paige Tester"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 5
Current value of {!MemberSchoolService}: a0l1200000AJIsxAAH
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa, Paige Tester, Allison Villa, Paige Tester, Paige Tester"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH]"
LOOP: Loop_Through_Member_School_Service
Loop Through: [a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]
Iteration: 6
Current value of {!MemberSchoolService}: a0l1200000AJIt2AAH
ASSIGNMENT: Mark_At_Depth
{!MemberSchoolService.At_Depth__c} Equals {!SetAtDepth}
{!ServiceMemberNames} Equals {!AddName}
Result
{!MemberSchoolService.At_Depth__c} = "true"
{!ServiceMemberNames} = "Paige Tester, Allison Villa, Paige Tester, Allison Villa, Paige Tester, Paige Tester, Allison Villa"
ASSIGNMENT: Add_Member_School_Service_to_Updated_Collection
{!UpdatedMemberSchoolServices} Add {!MemberSchoolService}
Result
{!UpdatedMemberSchoolServices} = "[a0l12000005NmuiAAC,a0l12000005NmunAAC,a0l12000005NmusAAC,a0l12000005NmuxAAC,a0l12000005Nmv2AAC,a0l1200000AJIsxAAH,a0l1200000AJIt2AAH]"
LOOP: Loop_Through_Member_School_Service
End Loop.
FAST UPDATE: Update_Member_School_Services
Update Member_School_Service_Term__c records whose IDs are stored in {!UpdatedMemberSchoolServices}.
Variable Values
[Member_Term__c=a0I1200000JYvo2EAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Paige Tester,Id=a0l12000005NmuiAAC]
[Member_Term__c=a0I1200000JYvnxEAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Allison Villa,Id=a0l12000005NmunAAC]
[Member_Term__c=a0I1200000JYvo2EAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Paige Tester,Id=a0l12000005NmusAAC]
[Member_Term__c=a0I1200000JYvnxEAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Allison Villa,Id=a0l12000005NmuxAAC]
[Member_Term__c=a0I1200000JYvo2EAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Paige Tester,Id=a0l12000005Nmv2AAC]
[Member_Term__c=a0I1200000JYvo2EAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Paige Tester,Id=a0l1200000AJIsxAAH]
[Member_Term__c=a0I1200000JYvnxEAD,School_Served__c=0011200001K6042AAB,Term__c=2016-2017,At_Depth__c=true,Service_Member_Name__c=Allison Villa,Id=a0l1200000AJIt2AAH]
Result
Failed to update records whose IDs are in {!UpdatedMemberSchoolServices}.
Error Occurred: The flow tried to update these records: null. This error occurred: CANNOT_EXECUTE_FLOW_TRIGGER: The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 30112000000LAS7. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.. For details, see API Exceptions.

We've been trying to determine what may be causing the flow error, but are uncertain as to what the message is conveying, are there are steps we may be missing. I can provide.

Hope it helps,