Thanks a lot for the feedback. Although I've received several bug reports like this, and unfortunately every time, it was the player who placed a flag incorrectly. So at the moment I'm more leaning to one of those 2 flags being incorrect. I think out of those 4 flags, the second from the top shouldn't have been placed.

But my assumption can certainly be wrong! To be sure, could you take a screenshot of a loosing screen? as all the mines will be revealed then, and we can see if the number is indeed correct or not.

There are a lot of bugs in that screenshot