if anybody runs into the same problem, as it cost me some time to figure this out 
in the UE5.4 VR Template i modified the IMC_Default Enhanced input settings such, that
instead of reading out a 1D axis for move to alter it to a 2D axis… makes it easier to include strafe and walking forward.
However when i do so, my motion controllers were not tracked any longer.
So what i did exactly:
i added to IMC_Default a new Mapping context IA_2DMoveAxis that binds the 2D axis from the oculus controller.
By this IMC_Default had then two ActionMappings (used or not) for a particular controller axis binding (e.g Thumbstick L Y, X would be linked in to IA_Move and IA_2DMoveAxis) - which seems to cause my not-tracking problem without raising any error message.
Deleting one of the double binded IA_ActionMapping ones → solves it - or just avoid a double binding in the IMC … 