Maven miniboss makes boss invincible

During the brain phase maven spawned the bestiary boss, the purple bear, who makes a lane with vines then charges down it, well, I think i killed the miniboss while it was charging, the vines failed to despawn, and became invisible. because of where they spawned, partially overlapping the boss, the boss became immune to damage. It may have just been immune to projectiles I suppose but i don't have the means to test that. suffice it to say this does brick the encounter comeplely as the invisible vines don't ever despawn.

Just happened to me as well. Literally everything I do this league turns to shit.