To improve performance, Piwik 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.

There are 2 solutions

  • 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:
    [Debug]
    disable_merged_assets = 1

Then, delete your browser cache and refresh Piwik: after a few seconds, it should display correctly again!
* If you still experience the problem, check that any Adblocker extension is disabled, as it may mistakenly block the Piwik Javascript or CSS files.