resistance on climbs

Hi there,

Tacx Flux 2, Fully unto date firmware and calibrated.

Very weird experience on the climbs when on zwift. On a sustained 6% climb I was trying to remain smooth and keep the same cadence and effort but the resistance kept falling away and then picking up every couple of seconds? Felt really strange like a slipping sensation? This means that the cadence and power are all over the place rather than retaining a smooth cadence and level power.

Kind of one pedal stroke hard then the next easy spin and repeat....Gradient remained the same as did my effort.

Seems OK on 4% climbs but anything steeper and this problem presents.

What is wrong with it and how do I fix please?

Please help, Kev