[solved] Usually showing "cannot display the web page"

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Hello,

I am using LiteSpeed 4.1.4. I usually got the "cannot display the web page" after a few hit to navigate, in front-end, back-end, phpmyadmin too.

I don't know why. But server is running normally, not disk i/o, not high load, in very fast state. Although, it returns error page the database is working and update my queries.