iOS: Random error message from iOS14 EXC_BAD_ACCESS thread Queue: NSManagedObjectContext NSInternalAdditions forgetObject propagateToObjectStore

The error suggested that there was a CoreData action done on a different thread that the one it should.

According to the doc, you can use perform() (async) or performAndWait() (sync) to ensure that you are doing the calls in the correct queue.

You use contexts using the queue-based concurrency types in conjunction with perform(:) and performAndWait(:). You group “standard” messages to send to the context within a block to pass to one of these methods. There are two exceptions:

Setter methods on queue-based managed object contexts are thread-safe. You can invoke these methods directly on any thread.

If your code is executing on the main thread, you can invoke methods on the main queue style contexts directly instead of using the block based API.

perform(:) and performAndWait(:) ensure the block operations are executed on the queue specified for the context. The perform(:) method returns immediately and the context executes the block methods on its own thread. With the performAndWait(:) method, the context still executes the block methods on its own thread, but the method doesn’t return until the block is executed.

When you init your context, it will be attached to some queue, and you won't know which one, but by calling that method (either perform or performAndWait) you'll be sure to do it in the correct one.