Abyss Unable to Complete

I just cleared a Spring map with multiple Abysses. One of them will not complete. I circled the entire area to see if there was a mob that got stuck somewhere, but to no avail. That one Abyss just won't complete. Leaving map now...

Just had this happen to me too.

Completed a Sun Temple map with 2 abysses.
One of them completed normally, the other doesnt.
I have full cleared the map, 0 monster remaining, the abyss still doesnt complete.