When running on our production server (which is internal only), EPiServer runs slowly once in a while. It doesn't matter if it the site or the CMS editor - once in a while both take some time (30-40secs) to complete a request. It happens for a while only (1-2 request become slower) and then the site runs perfectly. On my local machine I don't have such problems. The issue happens when there is only one user on the web site. Can you give me some points to investigate this strange behavior?
Have you checked the recycling settings of the application in IIS? Perhaps the application is recycling while its being used which would certainly create the effect you mention.
I would also look at any external dependencies/APIs that the site might rely on to render a page or pages as this can affect performance
You could try using a monitoring tool such as NewRelic to trace out any slow requests to find the source of the issue.
Let me know how you get on
Thank you for the advice. I checked the AppPool, but it seems fine. I will check this tool to research the issue and will write back here with the results :)