Well, I know I'm always reporting issues here that turn out to be my own mental short circuits - and perhaps this is another one.  In some folders, there will be one or two thumbs that remain constantly in a state of "Loading . . ."  If I open the same folder in Studio, the thumb shows fine.  Even in QU, nothing hangs or anything and in fact QU will load the image into the Queue and if I change or create a filter then the thumb will show (come to think of it - this seems to only happen to pictures that don't yet have a filter - but certainly even not to most of them.)  This one is certainly not a big issue, and like most things that happen to me, probably isn't happening to anyone else - but it is rather curious.