Minesweeper bugged

To preface - I'm by no means a very good minesweeper player, I just do it time to time and my average time on the beginner difficulty is around 30 seconds. However, I've noticed in some of my games there appears to be mines that the game doesn't indicate. Is this a bug or am I just bad at the game?

Example: https://imgur.com/a/7CgWrhb