Hexarotor in offboard, the UAV never catch the setpoint, circling around it


I do need some help to investigate the following log with a hexarotor
px4 FMU V3 (pixhawk cube 2.1) 1.6.5 in EKF2:

The UAV has already made great long flight and has a cumulative flight time greater than 24hours. In normal operation, the UAV fly in offboard mode but RC is always ready, just in case.

On two recent cases it has encountered the problem of trying to reach its setpoint circling around more and more wider :
The first time it occured right after we changed the camera gimbal for a twin model (same brand and model).
First we recalibrated the compas and it flew great for 15 minutes.
For inspection we had to remove and then put back the exact same camera (2nd one) and this is this log which is visible here.
In order to recover from the phenomen we had to switch to stabilized mode. We performed another calibration and it flew great again for 15 minutes.

However i’m afraid this problem might occurs again. What can be the cause of such behavior?

Tank you very much.