I have a ST20 and ST10. I use the Soundtouch app on my iPad, PC and Droid. Lately, I cannot directly access my speaker from my Droid with the ST app. If I connect via my iPad and start music Spotify on the iPad I can then control the music through the Spotify app on my Droid. But even then, if I open the ST app, it won't see my speakers. Also, I cannot reconnect the speakers from my Droid, only from the iPad. I find the ST app to be a very frustrating interface.
I can imagine that's quite frustrating! Have you tried signing out of the SoundTouch app on your Android, or even uninstalling then reinstalling the SoundTouch app? Let me know if you notice any improvement!
I have done the suggested things multiple times. They have temporarily worked, but none has been a permanent fix. The ST app is ok when it works (lacks some functionality) but it is VERY unstable. Moreover, the functionality changes (without notice or apparent reason). As I said, Bose hardware is super, but Bose should get some better software or it will lose in the long term, especially because Bose is not a low cost item. I, for one, would not buy another Bose smart speaker. I recently passed on an offer to buy a new ST10 for $100 bucks. And, I have owned and enjoyed Bose products for many years. I still have a Wave radio next to my bed. It's sad to see what's happened to a once innovative leader in home sound technology.