Watch firmware: 2v19, DFU 2v16
Android Bangle.js Gadgetbridge Version: 0.76.1a-banglejs
Apps up to date as of 2 weeks ago updating again now (should have done that first, sorry, but this issue has been going on through multiple updates for many months).
settings .65->.68, alarms .44->.45, weather .25->.26, message ui .74->.75
As folks above have said, manually disconnecting/reconnecting through GB on the phone or rebooting the watch fixes it but the watch freezes and remains unresponsive on a frozen watch face until then.