WordPress site does not respond until the web server restarts. Infinite loading

I have been experiencing this issue for several months but it only occurred very rarely like once or twice a week. But since yesterday the issue has become more frequently like happening every hour and turn into a real headache.

What happens is the site hanging while trying to load the page. It does not show any error. It just looks like its just taking time to respond.

See screenshot : https://i.stack.imgur.com/huVKs.png

But the site does not respond until we restart the web server. After we restart the web server The site starts working as it suppose to work. Previously this problem only used to happen once or twice a month. But since yesterday its just happening like every hour or even after half an hour.

We do not see any error in server error log. There are other WordPress and non-Wordpress site running in our server. They dont get affected.

We cannot replicate the error as we dont know what triggering the error.
I can see the following log files from my cpanel

Webserver error log : https://i.stack.imgur.com/ZTFln.png
Web server ssl error log : https://i.stack.imgur.com/mNp6s.png
Web server transfer log : https://i.stack.imgur.com/XqTIB.png
Web server SSL transfer log : https://i.stack.imgur.com/MzAPH.png

I do not understand properly what to figure out from this log

There is no particular time of the day when this happens. its just happening randomly.

PHP version in the server for this site is 7.2.16
Webserver – Apache
Database – My SQL 5.1.7
Wordpress Version 5.2.2

I have installed php Compatibility checker plugin. And its showing some compatibility error in contactform email plugin

https://i.stack.imgur.com/F8Fao.png

But I dont think thats is the reason of the problem. because we experienced this issue even before installing this plugin and when there was no compatibility error found by the plugin.

I am absolutely clueless where to begin.

Can you please give me any clue.

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