Im am currently dealing with the same issue. Cant fix it no matter what i do. Played with zombies for a day in game then switched them off until first blood moon. Completed the horde. Turned them back off. Approaching day 14 blood moon turned them back on and game was broken. No jumping, no dying even from falling from a massive hight, cant drown. Over encumbered with an empty inventory and no zombies either. Exit game and turn them back off and its like the glitch never happened