first time reading this thread.
seems to me, if you have a PUDDLE, you have a plumbing problem. That is a lot of water in a short span of time. Not possible to get that much water thru a wall leak.
Possible: your shower head is leaking from behind the wall, where it meets the pipe. When your diverter sends water up that line is when it leaks, and only then, and then you get enough to have a puddle on the floor below. Also possible: the diverter is leaking where it connects to the line going up to the shower head.
Possible: the p-trap and drain are leaking. Since a full tub empties out fast, while a shower lasts longer, this might be possible. If you plug the drain for your next ten showers, do you have a dry floor?
Look at the pipe going up to the shower.