When I moved a folder from Site 1 Doc Library to Site 2 Doc Library (modern experience in both, btw), I ended up with copies in both locations. Is this expected behavior, that it doesn't actually MOVE the files? Does this mean that the files in the new location will not retain their Doc IDs and links, as well? Thanks, in advance!
So it turns out that some of the files had locks on them or special permissions that were interfering with the internal "move" mechanism within SharePoint Online. I had to map SPO as a drive and could only COPY those last items to the new location. I then had to delete the original folder manually. HTH someone else! (BTW, I never received an error in SharePoint. It wasn't until I tried the "move" command from within Windows File Explorer that I got the error that the files "could not be read from" the source location. I tried a copy instead with just a single file, and it worked, which led me to then trying to just COPY the entire folder.