Discoloration noted at wall under the window sill.
As seen by infrared image flow of moisture noted from under the external sill. Ply wood is used under the window sill at external side & crack noted on it. Water seep-in noted from the plywood. Plywood makes the wood porous and susceptible to water damage. Thereby creating moisture path and causing discolouration at internal wall surface. If not rectified timely, moisture will spread and damage the entire wall.
We recommend chemical pasting of stone above the plywood with epoxy joint filling.