Where's the leak

In late June I noticed my water level going down overnight (pump off).  In early May I replaced the pump motor, same model just a bit more hp and everything was fine until late June.   In two weeks w/o running pump I lost over half the water.  The level is below the light, vacuum port and skimmer but above the side suction along with main drain.  I have filled the pool to half way up the light but there is no drop in level now.  Would the leak have something to do with everything being under pressure, “closed system” and once level dropped below leak and filled back but not a closed system due to not running pump because pool is not full?