The bathroom on the main level of my house leaks through the drop ceiling in my basement bathroom when it gets to a certain level in the tub. It doesn’t hit the overflow level when it does it. It’s only filled about a 1/4 of the way up before it dumps water through the ceiling. Why does it do this?
It leaks because there is a leak in the drain gasket and/or trap and or other parts of the waste and overflow drain connections. Fix the problems before you have a problem with wood rot. Thankfully, you have a basement under the tub, which will make the repair easier for you or your plumber.