I have the same issue, when I open one of my Onedrive/pictures/... folders, old thumbnails pop up and then dissapear in a fraction of a second to just show the icon. These thumbnails often have black bars top/bottom or left right. I have thousands of photos in my Onedrive folder on a second HDD, set to always available on this PC and fully synced to the cloud.
I have fully rebuilt my PC, updates all installed etc and ran all the error checks etc. Ondrive lets you map back in after the PC refresh to save re-downloading. I have tried all the above tricks several times to no avail.
Since all the thumbnail caches are on the C drive these have all been rebult so shouldnt be the source of the problem following a PC rebuild.
One fix is to view the file in windows Photos app, once opend the thumbnail and that of the images to the left and right then re-appear after clicking refresh on the view! The preview then also works.
As I have thousands of photos in hundreds of folders this might be time consuming so I am thinking of finding a screen saver/slide show option to run though then all.
And I have also just found this fix - Open Photos App and allow it to search for pictures in the Onedrive/pictures folders. The Photo app then searches for all image files and regenerates the thumbnails. - This is taking some time so be paitent. I noticed much of my time line was missing while it updates this is now slowly being populated.