See Invisibility isn't bugged. It's just bad.
Rather than being actual See Invisibility. It's more like "Investigate" whereby at the start of a character's turn, enemies nearby simply have to make a DC 13 DEX save to remain invisible (And given that not only is this encounter in Act 3 so is high level, it's also with characters that are DEX based so their DEX saves are very high)
As a result, the most effective means of countering invisibility, is to spam AoE effects - Especially ones that still work through saves. Such as Wall of Fire and Insect Plague.
With the most effective method being to have a Cleric wearing the Luminous Armour using Spirit Guardians (Radiant) - As not only does this ability provide a constant AoE that still deals half damage on a save, but the Luminous Armour means that any time you deal Radiant damage, EVERYTHING in the area (Besides allies) gets inflicted with Radiant Orb which prevents invisibility.
No, it really is bugged. I cannot investigate anymore. There is no check, no nothing. Simply removed from the game. Similarly, any see through invisibility items or effects do literally nothing. Whether it's an invisible object or enemy, it can't be detected through the intended means. However, player invis is bugged as well. That's because it's incompatible with half the status effects in the game -- arcane synergy, temporary hp, bless, you name it. If it comes from an item and has a name, it's incompatible. BOAL's blessing? Incompatible. However, if I inflict a similar enough status on an enemy, e.g. wet, they can't become invisible, either.
Throwing enemies out of invisibility has been largely "free" on my run, since I have someone focused on lightning AoE, but it's REALLY annoying with invisible objects. Any spell sourced or gear sources invisibility doesn't work for players (potions work somewhat, interestingly), but detect invis is just busted, no matter if spell, condition, or consumable. You're going to need a character in the party that can just knock them out of it whenever necessary.