The Cookie banners doesn't appear after the Agree button is clicked!
The first thing to check is that the browser is configured to accept cookies. To check if your browser accepts Cookies, please click your browser from the following links;
Internet Explorer
Google Chrome
Mozilla Firefox
Safari
If cookies are enabled then the next most likely cause is that there is a Javascript issue. It is possible to turn off Javascript in the browser, so check that the browser has Javascript turned on.
If Javascript and Cookies are both turned on and enabled, then there may be a conflict with some other Javascript running upon the site.
The best way to check for conflicts is to turn on the Java console, and observe the errors and warnings displayed when the cookie acceptance is clicked. The messages may help identify the cause of the problem, otherwise is may be necessary to start removing the other Javascripts one by one to find out which one is causing the conflict.
If the site is using standard caching this may also cause a problem. Joomla caches the a page the first time it is visited. When the user clicks on the 'Accept' button the plugin will attempt to redisplay the page without the banner. However, if Joomla recognises the page URL it may serve the user the version within its cache which is the page with the banner displayed. One solution is to disable the standard Joomla caching. Another solution (preferred) is to make use of an alternative caching plugin. One such that we have used ourselves is JotCache, which handles cookie correctly.
Note that caching can occur at many places both in the server and in the browser and any of them can also produce this effect.