All new mounts cannot be added to the addon.

[Stevespim]

Like other users have said previously, any new mounts from the last year or so cannot be added to the addon. Their checkbox will clear immediately,

[brittmonster]

I came to report the same problem. My BFA faction mounts work fine but stuff like the spring fur alpaca and the new Shadowlands mounts arboreal gulper and Dreamlight Runestag immediately disappear from the mount preference list.

[andersleet]

#29 I made this writeup to help.