Re: [MOD RELATED] Horses Don't Appear in Relationship Panel

"I have located the problem mod which causes the issue in the first place,... "

Did you? Great! Thanks for not sharing the name of it.

I ended up going through the 50/50 process myself, eventually arriving at this mod as the cause of the issue:

Neia - No More Relationship Culling

Not sure what the original filename is but just search "Neia". 

Unfortunately this hasn't been updated for several years, but removing the mod, and subsequently performing an interaction with a horse, restores the relationship and allows access to profiles.

May not be the same mod for everyone but this was my issue. 

Hope this helps!