This is a bug present in both 3.3.3 and 3.3.4 but it's spitting errors so I feel it's worth reporting here also. (Cross post from this thread)
If a player or NPC has an effect that is set to END, it will spit out an error "Script Error: [string "scripts/manager_effect_4E.lua"]:434: getValue: Invalid parameter 1" when they select next turn (or the DM selects next turn) and fail to move on from that players turn. It will also end effects with that effect early, or skip ending them at all. It really plays havoc and we've finally figured out what it was that did it. It's definitely the END end condition.
https://puu.sh/zbBMh/58412b05b5.jpg
EDIT: Actually END N does it aswell, just no the next round (so when it would be due to fall off).
I've attached a GIF to show it in action. https://puu.sh/zbBYt/5c73ae5971.gif