[FIXED] Upgrade to 3.0.0 fails

I have two identical instances of piwik. The first one uprades perfectly but the second one crash with

An exception has been thrown during the rendering of a template (".form-description is undefined: failed at .form-description; line: 6183") in “@CoreUpdater/runUpdaterAndExit_welcome.twig” at line 8.

What can I do?

as told by @robertharm: Deleting the plugin folder /plugins/InterSites fixed the issue also for me