Rugosa Boss fight Bug report

Bug Report ID: #2943786153
This map’s boss is a mermaid. The abyss encounter is in the boss’s room. When I clean all the monsters except the boss. The abyss hole is still open and waiting for the last monster to be killed. The bug is when the boss uses the animation fighting skill and hides on the outside map. After that, the mermaid never shows up again. By the way, my map's progress failed because of that, so I can’t finish the boss.