It also looks like avatars of magazines/communities from kbin.social as well as post thumbnails no longer appear on lemmy instances with subscribers, e. g. the following path (to a post thumbnail) no longer exists
This does not look like a temporary issue, but a persistent issue that effects all communities and posts that have been fedearated before the change.
Maybe it fixes itself, if old posts get edited/changed and/or someone edits the description or avatar of an affected magazine so that an update gets pushed.