Edit: thought this was only happening in hardcore, turns out it's happening in both regular and hardcore.
In hardcore, I am unable to get near any player without having my entire game de-synced. By this I mean, if I right-click something in my inventory, it will just say receiving. And the last few lifes as soon as I saw someone, it would happen and then I would die (presumably from the person I saw killing me).
If I am nowhere near players (as far as I can tell). I am able to pick items up, put my battery in my flashlight, etc.