Resistance drop off after 40 seconds

I have a Garmin Edge 520 - about 2 years old now and a new Tacx Neo2

Tacx set up for ERG mode.

I get indoor sessions sent by coach through Training Peaks which gets picked up by the 520 and goes into Training calendar.

In each segment of the session I'm  in, the set resistance is lost after 40 seconds - happens every segment Im in - drops off exactly after 40 seconds. Have reset both Garmin and Tacx - nil change.

Any ideas anyone