Fenix 5X+ with unstable Mass Storage mode

I use Garmin Express, Android File Transfer, Garmin MapInstall etc. but it's very flakey now.
It will suddenly lose connection even if I'm not touching it.
And maps installed on my Mac with Map Manager will look like they are installed successfully with MapInstall but they never show up on the watch.
When it craps out I have to reboot and fiddle with the USB setting, often several times, before it works again.

I spent some serious money on this Titanium watch so I really hope this can be fixed.