that is likely related to https://github.com/LemmyNet/lemmy/pull/5107, which limits the resolution of thumbnails.
the client you are using is probably only displaying the thumbnails to you, not the original images.
edit: this seems to include lemmy-ui as well
edit 2: raised a bug report for lemmy-ui
yes, if the ban was with content removal and they’re the top mod.
the filter is whether the user being banned is the top mod.