I have this error showing up at the top of my installation after I updated it.
/vendor/php-di/php-di/src/DI/Definition/Exception/DefinitionException.php(20): Recoverable Error - Object of class DI\Definition\ObjectDefinition could not be converted to string - Piwik 3.0.3 - Please report this message in the Piwik forums: http://forum.piwik.org (please do a search first as it might have been reported already)
I had to force the update via cpanel softaculous after the auto update generated a 500 error and failed