After updating my to Copter 3.4-rc6 (and previous) on a copter with it’s MavID set to something other than 1 (in this case set to 2) connecting APMPlanner results in multiple system IDs being seen, namely 1 and 7, then shortly after loses connection to ID7.
This results in no parameters being loaded although the HUD is still working.
Erasing the board by loading Rover then Copter again results in no change.
QGroundcontrol reports the same but continues to allow you to change parameters.
I seem to have a work around by running APMPlanner 2.0.20 which connects correctly and stays connected.
Then run 2.0.24 and it connects without the additional ID being seen.
All firmware updates were done with APMPlanner 2.0.24 and all updates performed OK.
I don’t know where the SYS-ID number 7 is coming from. You can remove it from the system by right clicking and deleting it in the Flight Plan view. You also need to select the system with “control this system” option in the Flight Plan view (its the Unmanned System Control) that you want to control in the parameters view.