My opponent leaked Bloons but didn't lose any lives.
When this happens, it's usually caused by server lag that's delaying the server message that tells the game your opponent has lost lives. This can also cause the game to not show you if your opponent has placed/upgraded other towers etc so they're likely seeing the rush being defended. Unfortunately, it can be quite common if the internet connection on either side is weak or interrupted, but it's something we're always working on, and we look to improve on it with each update!
Need more help? Submit a ticket here