Ran into a bug that I couldn't replicate, but I think it's indicative of the new FW being a bit rough around the edges (all the previous notes in this thread give a similar impression - many improvements to features, but a bit buggy).
I have a custom probe scale of 1:20, firstly when I went to select it, it said 1:1 but changed to 1:20 after I tapped it.
Then I turned measurements back on, but it was still showing measurements as if the probe was at 1:1. Took a hot minute to work out what was going on there...
Switching back to 1:1 and then to 1:20 finally convinced it to scale my measurements.