Drupal 7 not able to run cron after views/panels update
For troubleshooting cron.php problems found this: 

https://www.drupal.org/node/553430

Cron stopped running; logs say: &quot;Attempting to re-run cron while it is already running.&quot;

I have been able to trigger cron using the ultimate cron module, which is in beta.

Still don't understand what was going and didn't find the faulty module but the "attempting to re-run cron while it's already running" error msg has gone away from the logs.