Waiting for store to long and Gateway Timeout (504)

Hi guys,
I have a problem with NOPCommerce 4.2. Sometimes, my site opens quickly but it often takes a long time to open with "waiting for ..." message in browser and finally Gateway timeout (Error 504) occurred. I have this problem in both site and admin section. I Uninstall unused plugins and disable unwanted parts. no error log in log section.
Please help me to know how to resolve this problem.

Are you using any 3rd party plugins that connect to other sites (e.g. Feed Managers, Amazon connector, etc.)?

Check CPU usage at that time. Check worker process in IIS how many queued requests and which one is taking too long time.

Thanks for reply,
I uninstalled any unused plugin and i have not 3rd party plugin in my site. when this error happen hardware resources usage is very low.

Hi,
I installed SSL certificate and used https version of my site and this problem never happened again. Do you think there might be a problem with this part of program?