When I download audiobook metadata, the author/tags etc download, but the posters don't show up on the library page. If I head to the edit tag page, the poster is there, just not selected. If I select it, it shows up.

There are some comments on the Plex forum about this, for example this one and this and here.

I've tried clearing the metadata cache and data directories (completely) and after a restart, this still happens.

Interestingly, when I do a library scan, recent additions to the library (that also had this issue) that were fixed also show that they're searching for the metadata (spinning circle etc).

This was working until recently. Don't know if Plex introduced a breaking change or not.

This is an up to date Docker image of Plex btw.