Same here. Tried all that stuff as well. It doesn't happen when not attached to the debugger... but that's not exactly helpful. @milutz Do you have a simple use case? And have you filed a Feedback? I'm seeing the same, triggered by either RunLoop or Firebase, but always ending in the same Semaphore issue. ** Note: I CANNOT reproduce this if I run Xcode and simulator from an Intel mac running macOS beta.