It appear that QGC is now resyncing between operation.
This was causing the bl_state to be reset to STATE_PROTO_GET_SYNC
and loosing the state of (STATE_PROTO_GET_SYNC|STATE_PROTO_GET_DEVICE)
Change PID to 0x4b:
Holybro obtained their own PID and VID but APM did not follow
the PX4 convention of makeing the board_id (0x8b) match the PID)
Incorporated the Upstream Bootloader state sequencing checking change.
Change the usb cout to send all chars in 1 write.