Overgrown Shrine Map - boss killed, no map achievement, Maven stays trying to kill me with orbs

Tried the Overgrown Shrine Map with Maven watching and I killed the boss, I did not get the map achievement and Maven is still dropping orbs to kill me. There is nothing for me to kill on screen.

Playing a skelly mage, spectre, animated guardian build. Been in and out of map 4 times so far to see if there's still a monster in there to kill but my minions are not focussing on anything. All that happens is that Maven drops orbs on me which still damages me despite any monsters on screen.

EDIT: Scrap that, the boss is still alive but now has not health bar and cannot be killed! Still getting hit by the purple spikes but minons are not targeting and there's no health bar over bosses head.