My book 18TB, missing video icons

I used my book 18TB for the first time today, to move video and jpg image folders from other small hard drives, it went well, but I accidentally unplugged it, and several video folders now won’t show a thumbnail from the video folder.
Everything else kept the original thumbnail, all files are visible in the folders, but if I open the folder to select a thumbnail, it says nothing matches my search, and shows nothing. I have tried a couple of the videos, and they seem to play fine, it took 11 hours uploading the stuff, so I don’t want to have to do it again. If I can avoid it. I would be grateful for any help.

Try running CHKDSK in read-only mode (do not use the /f option). This may tell us if there are any file system inconsistencies.

Ok I did that, no problem found, it is only the folders loaded since I accidentally unplugged it, and those that were copying at the time.