Unable to complete The Silent Cave Unique map

Bug report reference number: 3.946.208.745
I experienced this in (the only) 2 silent caves I found yet. I killed all small essences, then killed the big essence boss in the middle, it dropped greater essences, 0 monster remaining but the map isn't complete, the map objectives still states to kill the imprisoned boss but there is nothing killable or clickable left. If I start a different map afterwards the Silent Cave counts as failed. Both maps I tried this with were corrupted (1 yellow with 3 mods, other blue with 2 mods) and area lvl 79