I accidentally noticed the wall paint bubbling in the finish basement. There is a shower stall right above it. So I stopped using the shower stall for a few days. Using the moisture meter to make sure it is dry. I went back using the shower once by myself. No further leak. The my 7yr started to use it. Immediate leak. He likes to use the foot to cover the shower drain hole so there are water accumulated. And he moved out the foot to drain all water. I assume shower drain is leaking, but why it only happens when there is some accumulated water. Regular shower doesn't incur the leak. I am puzzled. Checked the shower stall, no crack on fiberglass noticed. It is fiberglass shower stall. Thanks for the help.