Tacx Flux2 Power Spikes on iOS on iPhone

I have been using Zwift on Apple TV with a Tacx Flux 2 for a few years and no problem, however for a few unrelated reasons I have had to move the Pain Cave - which means running Zwift on my iPhone - I did a quick spin around Innsbruck (short loop) to test setup and going up the small “hill” I noticed the trainer struggled to hold the power - it would have resistance then nothing back to having resistance - really frustrating as it prevents getting into a rhythm. Any suggestions to solve issue?