Hi, we've had the very same problem on an App that we inherited. After recompiling under Xcode 12 we started having this very same error every time there was a call to a moc. Ended with encaplusated every call in performBlock or performBlockAndWait fixed our problem. Hope this helps somebody.

Hello, thanks for your feedback. I've submitted a bug report as suggested, here's the FB number: FB15590204