[Battons]

The problem with hitreg that a lot of people forget is that gmod runs off the original version of source and they didn't bother making sure the hitreg worked correctly because the game was always fully intended to be sandbox. It just needed gunplay that worked. Then you introduce lag compensation, custom addons, custom hitreg, and its all a hot mess of stitched together issues that you can't really fix without going back to square one.
EDIT: forgot to add in the hitreg got significantly worse a couple years ago for some arbitrary reason, after a quick google search its showing me october 10th 2018 is a commonly complained about update. So I hate to be the bearer of bad news but unless you wanna go vanilla or code your own hitreg we are kinda screwed for now.