Web php load so slow after long time (30 minutes) no use at Chrome.

I am having 1 problem with php web. My web using php 7.0 and httpd at Linux ubuntu.

When I browser the web at localhost, it working file. But after I deployed. The first request is ok. but if I not request the web long time, about 30 minutes. It take very long time to response. When I see at chrome console, it display pending.

After I waiting loading, ~ 1 minutes. The next requests are fine, very fast

I checked the code, nothing big query.

Here is my php config

Could you please help to give me some suggestions, thanks so much!

http://13.55.177.54/phpinfo.php