how to get images out of On1 and back into LR catalog

I've got a big mess, involving LR classic, an aborted and rebuilt sync, and a lot of succesful and unsuccesssful efforts to get back where I can see all my files.
I use LRC but use my IPad and phone when I travel. I have about 80K images in catalog -- images on external hard drive, catalog on IMac. As I travel a lot, over time I have accumulated 43K photos in synced photos. I recently returned from a trip with about 3K photos to sync. Process took days (there were lots of other photos resyncing -- I now know to remove ones from Synced photos that I no longer want synced, but I can't do that til I resolve the issue of the photos missing from where they were before the sync). The process hung up with 9207 photos remaining. I spent a couple hours on the phone with Adobe rep, who ended up telling me to rebuild the sync data -- which took me up to 43K photos syncing! And it was incredibly slow. after a few days, it completed the sync. When it was done, there were 9207 images on the IMac instead of on the external hard drive! I know to move things around via LR rather than in finder, but I've had a terrible time figuring out what files are missing fromtheir proper locations. Too many to go through them all using locate feature. In fact when I clicked on missing files and located them, often they'd disappear from the folder they were originally in (I think the files are there but the catalog no longer references them in that location). So then I tried moving files from IMac to proper folder on external drive, thinking that the photos would then be wehre LR expected to find them (ie where they'd been before the sync mess). That seemed to work for the most part but I didn't know how to determine what was still missing (and in some cases, it didn't work -- see below)
So I started checking for 1-1 correspondence between All Photos (sorted by month) with my folder structure (which is also sorted by month). Very tedious and not really working cause when the number in all photos is greater, and I select and move them all to the correct folder, some wont move. It doesn't say they're already there, it just gives me an error message saying they can't be moved.
So then I went to the folder (in LR) with 9207 photos that was created from the safety net from a Carbon Copy Cloner backup, which I'd moved (in LR) into the external hard drive to go through, thinking I'd be able to identify ones from a particular month and move them to the proper folder (with the rest of the photos from that month), but when I try moving them in LR, I get an error message. I've never had trouble moving before, and it's not telling me that they're already there, just that they can't be moved. Don't know if it's cause they're from a safety net from backing up or cause they've turned into On1 (see below)
I just tried moving one of the many files (that I've edited in LR and was in my catalog til this mess) that's still on the IMac to the 2018_9 folder on the external (My Passport drive). The image still does not appear in the 2018_9 folder in the LR catalog. When I search for it, it shows that it's in On1 Photo in that folder. I checked and this seems to be the pattern with many of the images that I'm trying to make accessible in lightroom. I've never used On1. How do I get photos out of On1 and back into LR?