Fatal error in Piwik 2.16.1

We have successfully upgraded from Piwik 1.12 to version 2.16.1.
The upgrade procedure we followed is the manual procedure indicated in Update Piwik - Analytics Platform - Piwik
First we tried keeping the old files but we had several errors during database upgrade like: PHP Fatal error: Class ‘Piwik_Plugin’ not found in /var/www/html/piwik/plugins/…
Finally we succeeded the upgrade by replacing completely the piwik folder with the new version and just adding from the old version the file ‘config.ini.php’.
The command used for the upgrade was: /var/www/html/piwik/console core:update

The application seems to work.
However, we have the following error in a widget used in a iframe in another application
Call to a member function getColumns() on a non-object in /var/www/html/piwik/core/Plugin/Visualization.php 350 using PHP 5.3.3

We have tried all the actions in the troubleshooting, included the uninstall of the two non-supported plugins. But we still have the error.
Any idea how to solve this ?

Hi there,

could you please create a bug report on our tracker: Issues · matomo-org/piwik · GitHub

and please post there the exact URLs where you get the error message?

Hello, finally we have found the solution. The widget displays without error in the iframe after having deleted %5B%5D after columns: