Upgrade Error to V3

Piwik upgraded to the new 3 Version but after updating I receive the Message “Class ‘Composer\Semver\VersionParser’ not found”.
How can I fix that? It was a standard Piwik installation just about 3 months old with no plugins etc.

It seems that it was discovered here: https://github.com/piwik/piwik/issues/10801 but no solution to it? How many others like me will have the same issue? Please come up with a solution for that.
When I do a a “php DIRNAME/console core:update” on CMD line is says “Everything is already up to date”.

So whats next?


Hi there, please make sure all files are uploaded corretly. Maybe re-upload all files from Piwik 3. Also check your Admin > System check - is there any warning displayed?