Loop in a mission is not working

We switched some time ago from Arducopter to PX4 with most of our drone models. Also the integration into our GCS was without issues. But now we have a problem which we didn’t manage to figure out why.

We are generating missions which are sent to the flight controller (cube orange). Initiating the mission everythings works as it should until it (the mission) reaches the point to loop to the first waypoint. This is not done, the drone keeps holding position and is not moving.

The way switching to another flight mode and back to mission for execution doesn’t work neither, as suprinsingly the mission is deleted after mode change.

Anyone with a hint on how to get the loop missions done?

Thank you