Avatar's viewpoint acts strangely when looking up or down

I’ve been working on an avatar on my own, but an issue I’ve found is that when looking up or down, the viewpoint stays at the same y-position as though I were looking straight ahead. I initially thought this was an issue with my VR setup, but the issue occurs in Desktop with the avatar, and most importantly the issue doesn’t occur on any other avatar. Does anyone have any clue as to why this happens and/or how I can fix it?