I used to experience the same bug on the 13.15 beta: Unable to configure data screens via Android app / extreme lag then disconnection
I just updated to 13.21, and apparently no fix has been done on this topic, I experience the same behaviour: impossible to configure the data screens on the Android app, then disconnections from the watch, until I restart it.
I don't see any mention of this fix in the 13.21 changelog but Garmin-Kevin closed the thread yesterday saying that it was now fixed.
Am I the only one?