ERG mode does not work with my new Flux 2.1


I have just bought a Flux 2 and I have interval training workouts through Training Peaks on Zwift.

When I try to exercise in ERG mode, I do not have constant watts.  Please note that I have been training on a trainer (Elite Direto and Kickr CORE) for three years and am familiar with these settings in Zwift and how it should work.

Is there anything to do?  Is this normal?