I see there are many issues with Tacx, but this one seems to be slightly different.
I have a flux s, zwift on the iPad, using companion app and an Apple Watch for heart rate. Most of the time it all shows to be connected and “controllable” in zwift.
When I begin a ride, the resistance does not match the hills in the road. It’s almost random, or delayed (hard to work out). On workouts the same thing happens. So the resistance changes and everything else works, power etc. Seems to be all fine. It’s just the resistance the trainer is outputting is random and I can’t work out why.