Prism
Explorer
Right...and this is why I have the attacker make the stealth check at the point he emerges from total concealment. It is to see if he has been able to take advantage of his targets distraction. If the target isn't alert or in melee I might give the attacker advantage on the stealth check. If the target is expecting the target to emerge from somewhere I'll give disadvantage to the hide check. If the target is readied and watching specifically that spot the check might automatically fail.
With you there. I might be a little stricter about the auto fail part though. If the rogue, in combat hides behind a wall and then pops out in the same round or even a round or two later I would say an hide attempts would auto fail as the enemies would be watching that corner - unless a distraction was created to help the initial hide "where did that rogue go?" or the eventual attack.
If the rogue moves out of the room and then comes back in from a different corridor then I'd be far more likely to allow the distraction to work.
If an enemy was stood in a good position to continually observe the room I would probably always allow them to automatically see a rogue trying to attack from partial cover - again unless a distraction was created