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

My fairly old RT-N66U has recently taken to the same issue where wifi becomes unusable and one has to power-cycle the router to fix it. I don’t know what to suggest about troubleshooting, but I went into the firmware and set up an auto-reboot at 3:30 am… If that doesn’t eliminate the freeze-ups, it may be time to retire the thing… It’s not like I made a configuration change that would have done it.