I have the same issue. I think it might be related to combat mods, yeah, but in my case it's the Kingsgkaive Bound Sword one. It is indeed a combat animation replacer. VioLens is okay, since I installed it in the very beginning of my Skyrim lifespan and it gives absolutely 0 trouble with any other mods. I'm using the Automatic Crossbows mod, and, yeah, all crossbows are affected when an issue like that emerges.