Shower Tub Valve leaking from behind cartridge
What you see in the picture is just water that was in your pipe dripping out.  After shutting off water, there is always a small amount coming out.

If the leak is external (in front of your tiles), i would say it is your cartridge or seals of your faucet being faulty.  If it is behind the tiles, the soldering of your pipe must have given up which is very bad news.  Is your cement board wet?

If you have another bath with a compatible faucet, swapping them to isolate the problem.  Else get anothe faucet to try it out.

On a side note, I noticed the Redgard water proofing layer didn't fully cover all the way to the edge of the hole.  You might want to touch up and make sure water don't go behind.  Usually water damage happens at these openings.