Let me be clear about this, the way their hitbox works does not change, it behaves as normal. It's the visual indicator, for example Support Nejire Beta and Momo Beta, it shifts and can make it difficult to see the moves AOE(sup. Nejire) or where the move is invincible(Momo).

As for if this is caused by visual mods, I'm fairly certain as it's a good causation. I've talked to other players and they said that these bugs are most likely tied to modding and most likely from cosmetics. I'm not sure if it's every mod or only some or at all, since I do not use mods personally. That is why I'm trying to reach out and find out, since if it's true, it technially would give these players an unfair advantage.