I highly reccomend that you contact Capture One support before taking any actions.
If you look inside your catalog using Finder (right click, show package contents) you may find a file like
yourcatalogname.cocatalogdb.backup.
Check the date on this file and see if it matches the time of your catalog upgrade; if so it is the backup of the catalog before upgrade.
To use it I would first make a copy the entire catalog so that you still have a good copy if disaster strikes.
In only one of the catalog copies:
- Delete the yourcatalogname.cocatalogdb file
- Rename yourcatalogname.cocatalogdb.backup as yourcatalogname.cocatalogdb
- Delete the Cache folder.
This should be useable with Capture One 10