Resistance lags during workouts from Garmin 530

Hi all,

Have a new Tacx Flux s and trying to ride a workout paired from a Garmin head unit. The resistance lags badly/slowly when under the target watts and when above, doesn't change at all - if target is 200 watts and you ride at 250, you stay at 250. Any ideas? Have reinstalled everything, new connections, calibrated, nothing else is paired with it and it is connected through ANT+ only. Any help muchly appreciated. 

Regards 

Paul