I made sure to read hopefully most topics about this issue.
1) The app seems to successfully run in background, I tested it this morning by triggering a quick time adjustment by pressing D. It successfully adjusted the time (RCVD appeared) and stored the location, I checked in the app
2) I keep the phone with me in the office during the day. During night (10PM -> 7AM), I keep the phone on Airplaine mode
3) For days I have never seen the RCVD indicator
4) Inside App -> Time Adjustment I have only 2 entries in the history: May 16 12:32 and May 15 18:32.
Anyone has any idea what's going on? As a last resort, I'm thinking to disable the bluetooth connection and leave it to sync through MB6.