It's either Immersive Patrol 2 Or, Run for Your Lives Or, Dawnguard Sentries Or,Convenient Horses Or, Sky UI Or, When Vampires Attack Or, Cutting Room Floor Or, Falskaar Reason: I had exact same problem, Which I never found a solution to, and these are the only mods you and I both have in common. But of I had to hedge my bet on any, I would start with Immersive patrols 2, as this is the mod that introduces travelling merchants, which could mess something up. I would then move to Run for your lives, and When Vampires attack, and only then check the other mods.