I think the monster not being removed from the board is the issue here, but it may be other things. As you can see, my adventurer is sharing a space with the monster. The HP displayed are those of the monster. Here are my stream-of-consciousness notes on the matter in case the issue is something else: battle_425059312 Lunging Hack from Cheap Fencer's Boots defaults to targetting allies only. Was unable to check if targetting enemies was allowed. It is also possible that an enemy (bottom corner) was either not seen as existing or was drawn when it shouldn't be, as I cannot target it. I think it is this latter as the game says I have less monsters remaining than are on the board. Also I was allowed to enter the space in question.
Just had a similar problem in battle ROSE 63 - took me an acid spray to realise it the wisp in the bottom corner was already dead. Edit: It is has actually been cleared from the board - I can move onto the space.