This has been happening fairly consistently for me. I am in melee within 3 or more enemies, hp gets below 50% and I press the button for a health potion. I hear the sound and the potion level goes down, but the potion does not take effect for a good 3 seconds. All other traffic seems to progress fine, enemies still swing at me and do damage. In fact they even kill me a good percentage of the time. All without the potion ever taking effect. There are times I use a potion and click to retreat. It takes about 2 seconds for my character to respond to the move command, even when I am not surrounded and there is a clear path. Yet even then it takes a couple MORE seconds before the potion takes effect.
Does this count as some sort of potion specific desync? Potions take effect for what 7 seconds or so? It is very disruptive for a delay that can be half that period or more, and especially strange when the rest of the action appears to remain up to date.
Also, I seem to notice this the most in these races.
Hitting mobs like a boss until the last seconds. Game stops some time after the 10 seconds remaining notification - "Oh, sweet, it ended", I still use the big pot and click to move away. Then the game resumes:
We only had 4 people to begin with, RoA Ranger, Ele Cleave Templar, Conduit Witch and Leap Slam Duelist.
Well that plan didn't work out. First our Ranger died in Prisoners Gate to Goatmen, then our Templar TP'd out right when we killed Weavers and had to do redo it and our Witch died in Vaal Ruins (last room of Level 2 xD). Well my Templar Buddy and me got some really nice Gear and just blasted through the rest of A2, started Vaal when the first group finished him and entered Sarn Encampment 10 Seconds after them. After that we just had sick clearing Speed since Duelist and Templar are the 2 highest DPS Classes at that point and pulled far enough ahead to stop as soon as we hit Lvl 30 (wanted to get that extra point :P)