Still not quite to a place I can test the "pet horse" in my factory reset save (no CC, no mods, no store content whatsoever, but all expansions and a handful of stuff packs--and I'll be deleting this to make a new clean game for any potential future patches, which I hope we get!).
But, I have discovered that I also have the glitch ec1ipsse has: my Sim is leaving work within an hour or two of going in. I wondered if it were because my Sim has the rebellious trait, but like ec1ipsse, I'm getting no message about why the Sim is leaving work. In fact, since I left Memories enabled, I've noticed I keep getting messages implying that the game thinks that my Sim's hours are over, while at the same time he's getting a decrease in work performance for leaving. In my case, this is happening in the future with the Astronomy career.
Something I've noticed is that just about every time my Sim leaves, there's a plumbot trying to scan him. I think that may have something to do with it: His "work" interaction is canceled to allow him to be scanned by a plumbot who somehow sees him there despite his being inside. It's just a guess, though; I don't know what would cause this in the various other, present-day, worlds. Maybe something's preventing "work" from taking precedence over "social interactions?" It seems like I've seen this glitch before, in the past--at least in terms of leaving work before it's time to leave.