The Nov 23 version seems to have completely broken thumbnails. At first I could see the 100x100 and 300x300, but no 200x200. After a Windows 10 reboot, I can't see any of them.
I've downgraded to the September 4 version (22.20.02), and thumbnails are working. Unfortnately, in the course of troubleshooting, I deleted the cache files, so they all (10,000+) have to be recreated.