I had to reboot my unlocked HG612 this morning after it had kept the same line sync for past 103 days. (BT Agent was killed)
The BT Agent (whatever it does) is now listed in the processes after booting up, but I've decided not to manually kill it.
The 301 VLAN used for TR_069 was deleted when I originally unlocked it last summer.
If I'm right, I suspect BT cannot manage and update the firmware on my HG612 due to the missing VLAN while the modem is operated in normal bridge mode.