Not something I've ever seen before, and I've been running 4K/200% for about 10 years now...
The icons ultimately come from the OS so I don't know why they would be a different size sometimes, unless something is interfering with things or the per-process icon cache is being corrupted.
For example, an icon-replacement tool, or Windows compatibility settings being turned on (they should all be off), could cause problems.
It's also possible something keeps generating events saying the filetype icon has been changed, maybe before the icon/registry data is fully there (or as it's being re-written again).
If you've already checked the compatibility/DPI settings, clearing the icon cache is worth a try, as a quick thing: