Again, I’m not entirely sure what you are trying to achieve using two different audio interfaces or how they are connected but random clicks suggest to me that the two different interfaces are not clocked together.
When you switch the AXR to ADAT mode it is probably getting it’s clock from the Focusrite which fixes the problem.
As implied by st10ss, Cubase needs to be told when it is getting an external clock that it can’t control (from the Focusrite). . . . . . .‘Normally’ Cubase is able to set the sample rate of the audio interface, but if the AXR is being clocked ‘externally’ from the Focusrite then Cubase can’t alter it and you need to let Cubase know that it’s clocked externally