A few months ago we started having issues with logged-out users getting cached elements (i.e. “Log in” text and link in header.php on a page. Only a browser reload or browser cache clearing would resolve this issue. After many hours of testing and debugging, we ruled out all of the server-side caching and making sure the HTTP header cache-control settings were correct, we eventually discovered that this behavior is being caused by a PHP session being set by the Ad Rotate Pro plugin. Disabling this plugin corrects this behavior.
We can provide a test account so you can replicate this behavior. If needed, we can provide a Staging clone and give you SFTP access to that.
We don’t know how to proceed, other than replace Ad Rotate pro with another solution. Please advise whether you can help us identify how to resolve this issue with your plugin.
AdRotate simply sets a few values in $_SESSION for Geo Targeting and/or preventing duplicate adverts per page.
That should not (and probably can’t) affect caching or anything else.
Isn’t the problem the other way around then? That because a Session exists your cache does something weird?
Please check the servers error_log for any errors, anything mentioning AdRotate or sessions is interesting.