When running an activity app on an Epix 2 device (and possibly Fenix 7 and others with the same/similar code base), if the user accesses the watch face/glances then the activity is stopped. The result of this stoppage is similar to that of a crash or a call to System.exit() in that the activity session is saved (and immediately shows up on Connect) and the state of the app is lost. However, the watch OS appears to "think" that the activity as been "suspended" similar to how the functionality should work because if the user presses the START button again from the watch face, the same activity is immediately displayed (without the user choosing from the activity list). But although the activity was "resumed", the app is in the initial state as if the user started the activity from scratch.
This does NOT happen on the Fenix 6 or any other watches one or more generations old. On those devices, going back to the watch face or glance/widget list simply puts the activity app in the background and keeps it running. And when you press START the activity continues on.
The workaround for this is to capture the MENU behaviour and not allow the user to view the watch face or glances but that limits the user's ability to view info/data the may wish to see in detail (sleep, body battery, weather, etc).
Hardware details: Epix 2, FW10.44 (also occurs on 10.43, 9.37, 9.36, 9.33)