The timer app on my Galaxy Active2 watch stops by itself. I have also noticed that, even when I have the watchface active, when the watch display reappears after being in a screen timeout for a few minutes, the timer app (which is running) appears.
Does anyone know (a) how to solve the timer problem, and (b) how to keep the timer app from displaying automatically, as I have a feeling this may be part of the first problem? Note that, in Settings, I have "Show Last App" set to "within 20 seconds."
For number (2), I'm convinced that the Samsung Timer app is designed that way. You can temporary get your normal watchface by pressing home. buttton.
At least the current time is displayed in the time app at the top. In earlier app versions this time used to fade after 2 seconds, so an improvement in newer versions is that it doesn't fade. However, the font size has been reduced (without obvious reason), so on my 42mm it's not easy to read.