I think I spotted it this morning - although on a different occasion.

Tonight I left my phone at 15% bat - so it was whining all the night with low battery beeps. This morning I put it on a charger with 5% but noticed that pebble is disconnected. On the way to the office I've turned on my BT headset and realized it cannot connect to the phone. I've checked BT - it was on, however showing only devices which were on nearby - pebble, headset and my BT speaker. In fact I have smth like 10 devices paired - they just disappeared from BT settings screen (I've seen such behaviour before though).

Any attempt to connect the phone from headset failed. When I initiated connection from the phone - it connected.

Attempting to reset BT (off/on) does nothing - pebble is still disconnected, headset still cannot initiate connection.

Looking into syslog I see kernel reporting l2cap_sock_connect: failed -115 and followed by standard rockpool's QBluetoothSocket::UnknownSocketError.

So it seems there's still a problem in the BT stack implementation on jolla, where when BT adapter goes into deep sleep - it cannot be recovered back into proper state.