The See Invisibility spell and similar effects (Volo's Eye) can be contested. The enemy has to roll a dex saving throw and stays hidden if they succeed. Since the enemies who use invisibility are usually rogue types with high dex, they are quite good at it and likely to succeed if you have used the eye/spell/eilixir on a character with a low spell save dc.
Just as an added note, but as stated above, aoe s which enemies cannot save against, are a reliable way to force them out of invisibility.
Yeah, which is why you know it's a bug when it works never, and especially when it doesn't work on invisible objects. Those are the real annoyance. I look in my log and no one's even rolling anything. What's missing is whatever prompt tells your game to start rolling to detect invisibility. That also means enemies can't roll to detect me when using the invisibility potion, though they go through the animation. The other bug might be that many things are counted as AoE that have no save when they shouldn't be, or its simply a byproduct of the issue that no one can roll anymore.
