On top of generators being uncappable and not sending supply, and spawn’s supply being unusable, OG keep also bugs out. Sometimes the grawl is immune to damage/conditions even after killing both elementals.
You can still kill him using siphon damage from necromancers, but it takes several minutes.
If you can’t locate the bug, I suggest upping the grawl’s hp and giving him a damage reduction buff based on the elemental’s hp. I.E. if the elementals have 100% hp he takes 1% damage, 90% hp he takes ~10% damage, etc. I suggest taking the average hp% of the elementals, as this way if one elemental bugs the grawl will only have ~50% dmg reduction. This’ll hopefully prevent him from becoming totally immune without changing the fight mechanics.