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Karan KeharKaran Kehar 

A new update on queueable was introduced in Spring 19. The update now only permits one future call to be made from queueables. When will this be enforced on orgs? We need to do some update in the code so please let us know as soon as possible.

AnudeepAnudeep (Salesforce Developers) 
Reviewed Spring'19 release notes and I can't find any reference to this update. The latest documentation (v49) also does not talk about this

Where did you come across this update?