Got a requirement like to calculate average in account based on particular record type of case. My requirement is:

I have a field called ARP in account currency. I want to calculate overall average of ARP field in particular record type called customer order whether Case details either new or add-on.

So I'm trying write a trigger a trigger.

Everything is working fine in sandbox but in production when i update any old cases it's not updating accurately.If i do update in sandbox is working fine.

And for example there is case with above criteria like 18.55.But it updating 6.55.When i check from random accounts it  is calculating average with all cases to a respective account.

When i try to create any cases with new accounts it is working fine.Please help me guys to sort out.

trigger ForARPU on case (after insert,after update,after delete) 
   {
       if(Trigger.isAfter && trigger.isInsert || Trigger.isAfter && trigger.isUpdate) 
    {     
        //It will call a static method called ARPUInsert in ARPUCases class.
        ARPUCases.ARPUInsert(Trigger.New);

    }
}

Handler trigger

public static void ARPUInsert(List<Case>  CaseTriggers)
    {
        /** 
         * This method is to caluclate average of all ARPU amounts with case have customer order recordtype
         * as well as case details with either ADD-On (OR) New Subscription and update in related account
         * field called ARPU. 
         * This method will fire only when any case with record type called customer order is created as well updated. 
        */
        Id recordTypeId = [Select Id From RecordType Where DeveloperName = 'Customer_Order'].Id;
        List<Account> Accountstoupdate =new List<Account>();
        List<Case> CaseIDs = new List<Case>();
        for (Case s : CaseTriggers)
        {
            if(s.RecordTypeId == recordTypeId && (s.Case_Details__c =='New Subscription' || s.Case_Details__c =='Add On') ) 
            {
                    // Loop through and add caseId's to the list.
                    CaseIDs.add(s);
            }
        }
        /** @Var CaseAccountIds - to get accountId's of cases with list called CaseIDs */
        set<Id> CaseAccountIds = new set<Id>();
        for(Case c : [SELECT Id,ARPU__c,accountId FROM Case WHERE Id IN :CaseIDs])
        {
            // Loop through and add AccountId's to the list.
            CaseAccountIds.add(c.AccountId);
        }
        /** @Var Accountswithcases-to get account details to caluclate average */
        /** @Var results-to get average of particular account based on the cases */
        List<Account> Accountswithcases = [select Id,name,ARPU__c  from Account where id =:CaseAccountIds];
        Map<Id, AggregateResult> results = new Map<Id, AggregateResult>(
            [SELECT AccountId Id, AVG(ARPU__c) average FROM Case WHERE AccountId = :Accountswithcases GROUP BY AccountId]);
        For(account a1: Accountswithcases) 
        {
            if(results.get(a1.Id) != null) 
            {
                // Loop through aggregate results array and typecast the average of ARPU and update in account level.
                a1.ARPU__c = (Decimal)results.get(a1.Id).get('average');
                Accountstoupdate.add(a1);
            }
        }
        if(Accountstoupdate.size()>0) 
        {
            // DML statement to update all the accounts related with cases
            update Accountstoupdate;
        }
}