I just learned the hard way that you should never move a file or folder that has been shared with you. Maybe there are times and places where you can, but in my case and that of many others for several years now a bunch of files and folders disappeared when I tried to move them to My Drive from where they had been shared with me.
Trying to get them back was cause for panic until I learned that you still have them — they are just “orphaned”. So you can do a search in Drive for
And then step through each result, looking at the Details info to see if they all have a Location folder associated. The ones that don’t have a Location are your orphans. They won’t show up anywhere until you add them back to your drive.
Seems like this should have been closed up awhile ago (how about a view of orphaned files sorted by when and an option to Undo the Orphaning), but it’s still there so don’t fall into it.