I have exactly the same situation. Debug is possible is on the physical device. Even reinstalling Xcode 12 doesn't help

After updating to beta 4 everything works OK.

The API worked OK for 3 months, but as of this morning (September 1) it is dead. The error message is "very useful": "The operation couldn't be completed. (WeatherDaemon.WDSJWTAuthenticatorService.Errors error 1.)" Has something changed? Do I need to set something somewhere?

Yes, I sent that one, but no one responded. Hopefully, they'll put it back up.

Next time I'll test everything properly before I post here. This dialogue is a standard part of every installation. There are other reasons why TestFlight doesn't report all crashes.