I'm having the same problem, and it's driving me insane! The iOS 14 simulator is the worst offender, where multiple daemon processes seem to crash when the simulator finishes launch, and then again when the simulator is closed. I reverted to using an iOS 13.5 simulator and, although I do indeed experience less crashes, they are still occur and are similar (they're all SimulatorTrampoline related). It's almost as if there's some common code in the daemons that is not properly checking the existence of source/destination objects before trying to interact and so you get a crash. I've submitted my sysdiagnose and simdiagnose reports, as well as examples in FB8702058, so hopefully Apple is able to figure things out.
I can get the following sequence to reliably happen:
With no simulator running, start Xcode 12 and load project.
Use the iPhone SE 2nd Gen iOS 14 simulator and run the app.
Once the simulator starts and completes its startup operations, you’ll get the following crashes: CalendarWidgetExtension, NewsTag, NewsToday2.
The app will run. Depending on your app composition, you will probably get more simulator daemon crashes.
Terminate the app.
Terminate Xcode.
Terminate the simulator. After a time (15 seconds?) you’ll get another crash: bulletindistributord. You may get other crashes when the simulator closes, but bulletindistributord is always the last.
The simulator instability began for me in the Xcode 11 line, where you'd routinely get maild crashes in the simulators. And this happened across multiple machines, each with different dev environments, so it's not just an isolate case for me. But Xcode 12 is now completely infected by the crashes.