Curling down of leaves can be a response to water stress. Since you feel it is getting plenty of water then it may be too much. Symptoms of not enough and too much can look the same. If too wet the roots die and or shut down and can’t take up enough water to replace what it is losing even though there is moisture in the soil. The leaves curl to reduce water loss. Make sure water is draining away from plant roots. If not, try to make corrections to the soil and area to improve drainage. Reduce irrigation to the area too if possible. Root rots usually occur in poorly drained soils. If it has already set in it will be difficult to treat or reverse the damage. You can inspect the roots near the surface for root rot. Roots start to appear soggy or blackened, and the outer portion of the root easily pulls away from the inner portion. You may have to replace the plants after correcting any drainage issues.