Class Joomla\Plugin\Behaviour\Taggable\Extension\Taggable not found

From Joomla! Documentation

Errors reported[edit]

Updating from a version below 4.2.0 sometimes leads to an error that says Class "Joomla\Plugin\Behaviour\Taggable\Extension\Taggable" not found. The result is the page is broken, see screenshot.

4.2.0 Update from previous version - Taggable not found.

Screenshot 2022-08-16 225922.png

Versions affected[edit]

General Information

This pertains only Joomla pages that updated to Joomla! version(s): 4.2.0

What is the cause[edit]

The cause of the issue is still being investigated. The autoload_psr4.php file is not removed on the update. The current state can be found in the GitHub Issue

How to fix[edit]

Remove the following file: /administrator/cache/autoload_psr4.php

The system will then generate it again and the error is gone.