Hello, @pietvarkevisser,
Please go to Porto > Dashboard, unregister the theme license, and then re-register it using the same purchase code. Afterward, navigate to Appearance > Themes and update the theme. If the issue persists, you can try updating manually by following the instructions in the theme documentation here: https://www.portotheme.com/wordpress/porto/documentation/update-theme/
Best Regards,
PThemes Team.