I think I saw something similar, but I’m not sure if it covers your case. This was that it reverts back to autosense after screen is locked. And solution was to turn off haptic feedback plus something else. But beats me if I know exactly. I’ll try to dig it out, it has to be somewhere on the forum.
Edit: I have no clue what I remembered 
Anyhow, check this topic:
https://forum.hearingtracker.com/t/extra-programs-in-myphonak-marvel-2-0-app/47020/
And this post (or whole topic)
https://forum.hearingtracker.com/t/questions-about-phonak-apps/47739/12
So if there comes some notification or your keyboard plays clicks, that could kick HA which are connected with BT to transfer that sound, even if there is no sound (like with some websites, you have media volume at zero but intent will be sent and caught by HA) and they switch into streaming mode and after that stops, back to default - which is autosense.
Unfortunately we can’t see the log files of switching to be really sure what triggers it and in which sequence they go.