Firstly, when you experience this issue please check that any Adblocker extension in your web browser is disabled, as it may mistakenly block the Matomo (Piwik) Javascript or CSS files.

If after disabling all adblockers you still experience the issue, read on.

To improve performance, Matomo tries to automatically combine all CSS stylesheets and Javascript files into two large files, instead of having to download 20 individual files. However, on some webhosts, PHP scripts have a max execution time and if the server is overloaded, the script that merges all files together can take more than the time limit.

  • Ask your webhost to increase the max_execution_time in your php.ini file, for example to 30 seconds.
  • If you can’t change this setting, you can alternatively disable the feature to combine together CSS and JS files. To disable this feature, edit your config/config.ini.php and add the following:
    disable_merged_assets = 1

(if you are using Matomo 2.4.1 or earlier, set this setting under the [Debug] category)
Then, delete your browser cache and refresh Matomo: after a few seconds, it should display correctly again!

Previous FAQ: Matomo does not track visits on SSL / HTTPS pages.