Abyss pits are not opening in maps

Encountered this bug 5-6 times today, the map is cleared, monsters remaining: 0
one or more pits are not progressing to the "release monsters" stage

video:
https://drive.google.com/file/d/18Kof7BUquhWqisJ_SGxtrBe4peIoSjC1/view?usp=sharing

screenshot of the same issue earlier this day:
https://drive.google.com/file/d/1_BcW9UPaTD84CSTNi6-T4ez495akFzKc/view?usp=sharing