As I said, this happens after Archive invalidation, not because of in-game buffs.The speed doesn't change to huge values, but to enough to start pissing me off. It's happening with all horses: original one, wild and from mods. And yes, I have mods that change the look of horses or add new ones, but nothing more. I tried to disable mods, but it didn't work :( But if you disable invalidation, everything returns to normal