Drone drops out of mission mode by accident and switches to manual mode

I randomly (maybe every 10th flight) encounter the issue that my duo tailsitter drops out of mission mode for no reason and enters manual mode (pixhawk 4, FW V1.11.3). I am able to continue the remaining mission in QGroundControl. Here is a sample logdata where this issue happened (approx. 4 minutes after takeoff):

Any hints are very welcome, thank you very much in advance!