Some Art Not Syncing, MySQL Setup

Here’s my situation:

I have a machine running Kodi on Windows in the living room that serves as my “main” Kodi machine. I have a MySQL server running on a Debian box to sync my Kodi library between that Windows machine and two Raspberry Pis in other rooms. (There is no Kodi instance running on the Debian box, just the MySQL server.) The Raspberry Pis have had Kodi freshly installed with LibreELEC.

I’ve run into a weird issue: all the art on my Windows Kodi instance is fine, but both Raspberry Pis are having trouble grabbing artwork. Here’s the pattern I can find:

Artwork stored with the video files shows up on the Raspberry Pi fine.
Artwork I grabbed manually on the Windows box through Kodi’s “Choose Art” dialog shows up on the Raspberry Pi fine.
Artwork that was automatically grabbed on the Windows box and not manually changed somehow is not showing up on the Raspberry Pi.

If I manually refresh the info for a show, it loads artwork, but not the same artwork that’s on my Windows box–it just loads whatever the top result from thetvdb is.

Here’s a debug log, if it helps.

Any idea what’s going on? Have I done something wrong, and how do I fix it? It’s annoying to not have the same art on all my systems, but it’s REALLY annoying that the Pis aren’t even grabbing art at all for most shows.