Looks like a standard 4x5 VO2max workout. What was the name?
Did you happen to view the workout in Workout Designer before riding it?
It should look like the top chart which is how the workout should have felt if your signature is valid and the Tacx unit is within +/-1% accuracy as claimed.
The second chart shows a very hard workout with BT moments on 4th and 5th intervals and a difficulty level off the chart (unreasonably so). That would boost XSS significantly.
Has your crank powermeter been calibrated and zeroed recently?
You mention a 20 watt difference in a post above. That would certainly skew the results.