How to test that BLE connection is still active?

Product: Airborne Night

I am controlling a small swarm of mini drones through multiple long range BLE antennas: http://drop.marcotempest.com/A5N0

Once in a while a BLE connection terminates without a proper disconnect.

What is the best practice BLE command to send to the drones to inquire about connection status while drones are still on ground?

Thank you

I have same problem with mambo.
It won’t land regardless of landing command.
Would you share this solution?