So - because of other competition and work, I tried the baseline ride for the first time on Monday, 13 Sept.
The ride was going fine, then shortly after the start of the sprint / short effort, I lose all resistance. I write it off, it’s late, so I’ll do it tomorrow. (Today, Tuesday 14 Sept) Now EXACTLY the same thing happens at exactly the same spot. I was able to ride fine afterwards, I do sprint efforts all the time with fastest segment points racing - I don’t have anything to explain what happened here.
I’m using a Kickr Core - I’ve done extensive racing with it for a year, and I think this is the first time I’ve seen this problem, and it happened twice on the baseline ride.
I was recording to do a video of the baseline ride - so I put together the two segments, you can see it here: Baseline Ride Resistance Failure