FTP Short test problems

Hi I am trying to do the short FTP test and everything is fine in the low watt warm up but as soon as it asks me to go higher than 170w the ERG just fails. 

I have tried another workout (Jons Short Mix) and that was fine, no ERG problems up till it froze just before the short high watt interval. 

I have tried everything I can think of, my Tacx Vortex is calibrated and firmware updated, Zwift is updated and I even changed the tire as a friend thought it was way too stiff but keep getting the same issue. Any suggestions??

That sounds like it might be this issue. Right now the best workaround we have, while keeping controllable resistance, is unpairing and repairing when it happens. Some people don’t like doing that though since it can mess up their workout flow, and prefer to lower the trainer resistance in the settings menu so the automatic changes are less severe. We’re actively working on this issue, and if you have this happen consistently we would appreciate it if you wrote in an email to support@zwift.com so we can get some additional information to look into it further.