I bought a Vortex specifically for off season training in Zwift last year. It was fabulous. Stored it for the season, pulled it out a few weeks ago to start off season training (for me that just means working out/maintaining fitness over the winter) and calibration no longer works (using the Tacx calibration app).
Went to the Tacx support website and turns out Tacx did an update due to some issue (overheating??) and now to get it within the calibration zone the tire has to be so loose it slips (to prevent overheating is the speculation). You can calibrate at the high end, but that causes it to become incompatible with Zwift. With it calibrated at the high limit it reduces your RPM to nothing (44 for me tonight in Richmond!!) and reduces your speed accordingly. As such you can neither ride with others nor can you try to maintain a fitness program consistent with either real riding or rides prior to the update (or on other smart trainers).
I am doing everything exactly as I was last year and have read all of the “fixes” here, the Tacx forum and every other site on the internet; no go. My settings in Zwift are fine, using the same ant+, etc.
Note also that the forum indicates there are no plans to fix this issue. If you are a tech person and know how to roll back the software, go for it. Otherwise I cannot recommend tossing $550 at a company that won’t support their equipment.
(However, I will say that I still think Zwift is a great way to stay fit in the off season/winter. Still recommend Zwift, just not Tacx)