ASUS Wi-Fi Fails Daily - How to Troubleshoot?

The (internet/ wi-fi) connection is failing often. A router power-down fixes it. When the problem starts, I have pinged the router, showing varying times of 2ms - 300ms. Normal time is 2ms-3ms.

How can I determine where the problem lies?

Thanks

ASUS RT-AC56U
Firmware Version: 1.5.0_384.6