Currently running Copter 4.0.3
I am communicating via MavLINK and having an issue where I never receive an ACK sporadically. I have a Jetson Nano connected via serial directly to the TELEM1 port on the Pixhawk. The two areas where I am seeing this is when I send a MissionClearAll and a CommandLong(MAV_CMD_DO_SET_MODE).
First the Clear All case: I am preparing to send a new mission and first am going to clear out the old mission. Generally this works and I will receive a MissionAck shortly after sending the MissionClearAll, however sometimes I will never receive the ACK. I do see, however, that shortly after the current mission is cleared from whatever it was to 0 which leads me to believe the Clear All was successful.
Next the Set Mode case: I am trying to switch the autopilot mode (does not matter if going to AUTO, BRAKE, LAND, etc) and am sending the CommandLong(MAV_CMD_DO_SET_MODE). Again, generally this works, however sometimes I never receive the CommandAck. Despite this, I can see that the autopilot mode actually changes to the requested mode.
I am not sure if this is a bug or if I am somehow missing the ACKs. Either way, I can develop a workaround by also listening for mode changes and current mission changes in case the ACK is missed.