Thank you for this post. I have spent a week trying to debug this and consistently see the same behavior.
The hair cache when importing into 5.4 works fine, but when importing into 5.5 it generates the groom asset only. For some reason the code to generate the hair cache thinks that the groom generated from exactly the same file is incompatible with the cache. The error indicates that the cache code expects one less vertex per curve, which looks like a bug.
I’ve also tried importing into 5.4 and then converting the project to 5.5. This gives us an animated hair cache in 5.5, but some of the curve points are in a wrong position. My guess is that’s the points that current hair cache code is somehow ignoring.