To make it short it’s nutrients burns.
To understand why, it’s because the EC of the soil is too high, the tonicity of the soil turn into an hypertonic condition where the osmosis pressure from the cells membrane of the roots is reversed and fluids gets sucked out from the plant.
In response, the plant will increase its production of THC, it’s actually called an "EC precision stress". Just make sure to let the plant break down its nutrients before harvest. A 2 weeks flush might be required to avoid any hay or chlorophyll smells and tastes, making harsh smoke and black hashes.