This has happened two times in the last week. I have a Venu. I finished a Garmin coach run. The screen that lets you save or discard the workout showed. I left it like that for a bit. Then the watch buzzed, and when I looked at the screen it displayed the description of the workout (text). Tapping the screen did nothing. When I then pressed the lap-button, the watch asked if I wanted to START the workout (which I’d just completed). I pressed “no”, and the screen went to regular watch face. No sign of the completed workout on the watch or in Garmin connect.
normally, the “save or discard workout” screen stays on until I press save.