RFD Datalink + Pixhawk Servo delay and not smooth

Hello there,

I have some issues with my servos since they are not running smooth.
I think the problem has to do with either the Pixhawk (6X), the RF Design datalink or the combination of those 2. The servos run smooth and as they should with an servo-tester and also if I use an other receiver module like FRSKY.
Do you have any suggestions where the problem is? I’m using RF Design 868 module with an FRSKY.

Kindly help if you have any idea or solution
Thanks