Cover Art not showing for audiobooks

Server Version#:1.18.2.2058-e67a4e892 (Synology)
Player Version#:6.5 (iOS)

I have re-added a library that contains M4B audiobook files. For some reason the cover art is not showing on any files - it was previously showing before the library was removed.
The library type is music, and the advanced library settings are

Include in dashboard
Checked

Album sorting
Library default

Prefer local metadata
Checked

Store track progress
Checked

Include related content from shared libraries
Un Checked

Artist Bios
Un Checked

Album Reviews and Critic Ratings
Un Checked

Popular Tracks
Un Checked

Concerts
Un Checked

Genres
Embedded tags

Album Art
Local files only

Scanner
Plex music scanner

Agent
Personal Album Artist

i have added the library again and the album art is now showing…no idea why it didn’t work the first time!