>>1498727There could be multiple reasons why thumbnails aren't properly visible.
Some system optimization programs like CCleaner have the option to delete the thumbs.db.
If something like that happened, you can normally get them back by waiting until File Explorer has regenerated the thumbnails, which might take some time for folders with lots of files.
Some files, like certain video files don't generate thumbnails properly, so you need a third-party extension to generate them like Icaros.
>>1498733If it's just slow, but otherwise functional, you're probably out of luck because thumbnail management is a function of the operating system.
https://en.wikipedia.org/wiki/Windows_thumbnail_cacheHow many thumbnails are you trying to view at the same time? Unless you're waiting for 100 4k image to load simultaneously, it should not take longer than a few seconds.
