Follow up. Turns out my issues was local to my catalogue. They asked me to reproduce the issue and send a new round of logs. I followed my full upgrade process - Verify the catalogue, back up and the upgrade. The surprising thing was there was a verification error. I though my catalogue was error free. After fixing it said it was OK. I tried Verify again and it found another error, I fixed that. Then I tried again and it was OK. So, my catalogue had three separate errors that took three tries to resolve.
After that upgrade worked. Yay. I have had a few days working with it and I imported a couple of sessions I created while I waited and all is well.