After I did the factory reset a few weeks ago everything worked fine for a few days, but then my watch would seemingly freeze again. Disconnecting it from the phone in Gadgetbridge reliably cured the condition.
Then I did not use the watch for a week and did not connect it to my phone either. The watch did not freeze a single time.
When I connected the watch to my phone, I experienced occasional freezes again.
Two weeks ago I changed my phone from a Fairphone 2 (nearly 7 year old hardware) to a Fairphone 4 (recent hardware) and I did not experience any freezes since then.
This led me to the conclusion that the cause of the freezes may be connected to the Bluetooth connection. I think the connection was quite unreliable with my old phone.
Is it possible that an unreliable connection causes a deadlock on the watch when the connection is lost during data transfer between Gadgetbridge and the watch?