When chasing nuisance leaks like these I'll always dose the pool with a good amount of chlorine (5+ppm) and turn the pump off for a few days to let the pool stabilize at the level of the leak.
When they stop at the bottom of the tile line or the skimmer you'll usually find the leak in the skimmer throat or in a lamp conduit.
I've found quite a few nuisance leaks in the conduit of the lamptail below the JB of the switch or the switch leg at a coupling that had a near equal elevation as the leak in the pool. This can be a long way away from the pool itself.
I'm really shocked that American hasn't had any luck locating your leak, I've found our guys there to be awesome in finding leaks I couldn't find myself.

See Ya,
Kelly