Core Data processing crash

I see the following crash in CoreData iPAD running iOS 14.X. I am not able to find the reason for this.

Fatal Exception: NSInvalidArgumentException
0 CoreFoundation 0x19b6685ac __exceptionPreprocess
1 libobjc.A.dylib 0x1af6e242c objc_exception_throw
2 CoreFoundation 0x19b6d74cc -[__NSCFString characterAtIndex:].cold.1
3 CoreFoundation 0x19b6e3db0 -[__NSCFSet addObject:].cold.2
4 CoreFoundation 0x19b572fd8 -[__NSOrderedSetSetProxy member:]
5 CoreData 0x1a1735cf0 -[NSManagedObjectContext _processPendingUpdates:]
6 CoreData 0x1a1726edc -[NSManagedObjectContext _processRecentChanges:]
7 CoreData 0x1a172e48c developerSubmittedBlockToNSManagedObjectContextPerform
8 libdispatch.dylib 0x19b266ac8 _dispatch_client_callout
9 libdispatch.dylib 0x19b26dc08 _dispatch_lane_serial_drain
10 libdispatch.dylib 0x19b26e734 _dispatch_lane_invoke
11 libdispatch.dylib 0x19b278528 _dispatch_workloop_worker_thread
12 libsystem_pthread.dylib 0x1e1ec0908 _pthread_wqthread
13 libsystem_pthread.dylib 0x1e1ec777c start_wqthread

Can some one help me to understand the issue here?