I use the build it yourself Dexcom app on my Samsung s10e, and it works great. I too have had issues when restarting or starting a sensor. The solution is to uninstall the app and then reload it. The point of this is that you don’t have to download it again, the apk is still on your phone. Go to files, storage, downloads, and you should see it there.
I run the Dex app and xdrip+, with the xdrip+ receiving from the follow part of the app (not draining transmitter battery any faster). Data still goes to Clarity for analysis, but I love the way xdrip is more predictive of glucose readings, warns for lows, and customization of snooze on alerts. Also works nicely for my Galaxy watch (very cool).
Mike