Abyss last pit doesn't close/unfinished

As indicated here in this bloodwood map, I just encountered a situation, where there is a remaining pit, that remains open. All monsters in the map have been killed, and I have circled the map again in search of any stray monsters that might have been stuck somewhere, but found nothing. For whatever reason, this pit just remained like this.

Encountered same issue on Lost Towers map. THe pit itself doesn't really show up visibly, its only showing on the map itself as still open.