[Milhouse]

Code:

LibreELEC:~ # ls .kodi/userdata/
ls: .kodi/userdata/playlists: Structure needs cleaning

Now I don't know how to fix this. Usually I'd run something like e2fsck -fv against the partition on another system, but I don't know if this will work with libreelec's squashfs?

This isn't the squashfs partition, it's your ext4 partition so running e2fsck should fix it. Normally fsck should run at startup to fix minor errors, unless you've disabled it.