I'm not from Microsoft nor am I computer guru.
I've had the same problem with viewing my photo thumbnails. Countless experts later and the problem was not fixed.
So, here is what I did that actually fixed the problem.
Open your ONE DRIVE APP. Find the photo album you want fixed (one folder at a time), Right click. Go to more options at the bottom. Copy.
Go to your FILE EXPLORER. Find the corresponding file. Right click on it. Hit paste. Hit skip...and once transfer is complete, open that file and it should be good.