I had something like this happen on IOS. I added an unsupported switch, in my case, 5 minutes later, I had all my sensors vanish on the App (although I don't remember it reporting offline). I tried everything to recover, I even uninstalled the app. Finally something worked; Here is how I recovered:
1. Remove a sensor (in my case it was a switch that had been working fine)
2. Add the sensor back in.
3. Now "magically" all my sensors reappeared with "invalid" icons. I could not control anything with the app.
4. Trigger/toggle each sensor using the UI on the A+. As I did so, each sensor came back with proper icons and I could again control them using the App.
5. Joy returns to my life
Not sure if this will help, but it fixed me.