Please make an issue[github.com] with a HugsLib log from when you saw this happening. I haven't noticed it, and there's no reason to believe this mod would cause that.

Sorry for the late reply, Steam doesn't notify workshop authors when people create discussions.

I know, veeery late response, but for those who see it in the future, this is a feature of Yayo's Combat. It randomizes melee damage so you'll see melee weapon DPS change constantly. You can turn it off in the mod options.

I don't know about the negative armor pen though, sounds like a conflict with a modded weapon.