Windows can't make icon preview thumbnails of files it can't decode. So nothing may be broken here.
What I find is this leads into a long discussion about file content and what native Windows can decode.
To be clear, I'm talking the other issues than what you read in prior discussions from https://www.google.com/search?q=why+doesn't+windows+show+thumbnails
How do you fix icons and thumbnails from not displaying in file explorer?
Already Unchecked always show icons, never thumbnails in folder options. Tried deleting iconcache. Tried copying files from old user into current user folder. Sometimes icons and thumbnails display in some folders, and sometimes they don't show up.
OS: Windows 8.1 Pro.
TIA

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