I had this problem in the past and there was some kind of mismatch in the thumbnail size that resolved the problem but I noticed the thumbnails became blurry again a while back and am looking for advice to fix it again. The problem became very apparent to me in comparing the thumbnails at my Artstation account vs. my website. I’ll put a couple screen shots of the thumbnails below.
Ah.. so I messed with some settings, really just changing them and changing back to 300 pixels and now my home page thumbnails look great and are showing at 300 pixels but when I do an inspect on the shop page it looks like they’re actually appearing at 218 pixels. Not sure why and I haven’t found where to change/fix that, but that’s probably the issue.
I’ll check on some other devices, but it seems like Litespeed may have been causing a problem. I disabled the plugin and the shop pics looked great then re-enabled it and they still look great sooooo… I dunno. Hopefully they’ll stay this way!
Sorry for the horde of posts – wish I knew exactly what I did but I also just noticed on my dashboard page a message at the top that indicates thumbnails are being regenerated. I played with a bunch of settings (just changing to another value and back) so am not completely certain what really fixed it.