heyo! i think i've got something of a bug. I've got this on both PC and android but i'm only noticing the issue on android. sometimes on stage 3 of beginning sweeper, you can flag all the mines and it goes to -1, then the stage is no longer beatable. not sure if any other area of the game does this but it's the easiest way to reproduce it.
Hey, azlech. I think you actually do have one more flag than there are mines left on the grid here. The flagged tile directly above the red tile in your image is where there is NOT a mine. Remember, tiles without numbers means there are 0 mines around those tiles. I hope this helps you on your minesweeping journey.