RT-AC88U Hangs

Hi,

Sometimes, my AC88U router GUI does not respond to web requests (Administration)
This situation is not resolved until I restart the router manually from the switch.

During the problem, the GUI is not accessible from LAN or WAN, however, access to/from internet is not cut down.
So, all LAN clients can access WAN, and from WAN I can reach my LAN server. But I can not reach the router GUI.
Today it occured right after I accessed the GUI. before my access was cut, I saw the usage on CPU...

RT-AC88U Hangs