Citadel of Copper boss inaccessible after respawn

I just did a citadel of copper map. I had the boss frozen and stunned while he was doing the red slam attack. He managed to finish the attack moments before my last last hit killed him, so I died and very shortly after he also died waiting for me to click on him to finish the encounter. I respawned as I had one left, but the boss arena was inaccessible. All the the other content in the map was still accessible there was just no way to access the boss arena anymore.