My friends and I have had the same "ping randomly jumps to 150 and stays there until the game ends" thing. Definitely happening server side, it happens to all of us. If it's TDM you can leave and rejoin and that usually fixes it, but in quick play you obviously can't rejoin. Hitreg has felt messy to me since I started playing on release, but it feels like it might be getting worse. Today I had a lot of weird input lag and times where my weapon, melee or ranged, went into an enemy but didn't do anything, despite being at 40 ping. The shields blocking attacks from behind happens in single player too, I think, but my friends and I all have encountered it, it's particularly common in captain mode when you're attacking a shield wall from the rear and are on a horse moving quickly.
