Matomo is slow! It takes a long time to load widgets, reports and pages. FAQ - Troubleshooting

There are a few possible reasons that Matomo (Piwik) could be slow to load:

By default, Matomo reports are processed when you request them in the User Interface. Please see How to setup auto archiving of your reports every hour? to automate the generation of Matomo reports.
If you are using Matomo on a website (or thousands of websites) tracking millions of pages per day, please check out the doc: How Matomo for high traffic websites.
If your server uses NFS-mounted storage (for example if you are using OVH mutu webhost), widgets might load very slowly even if you are not tracking a lot of data. This is because Matomo by default uses « file based sessions » which are very slow when using NFS storage. The solution is to change a setting to enable Database session storage.