"Photos" loops continuously after Catalina install

I recently installed macOS 10.50 Catalina on my late 2015 iMac - seeming without issue. On my first launch of Photos it began some type of conversion. After selecting Library/Photos it has been repeatedly cycling between "Gathering Favorites," "Analyzing Scenes," "Detecting Duplicates," "Curating Bet Photos" and "Composing Layout." This has been going on for over an hour with the progress bar not moving beyond about 25%. I have 51,000 photos and 1,700 videos. Is this just a very slow process or is something wrong? Suggestions would be appreciated!

SUZSM