Hi Jesper,
Sorry to hear about that, but ConvertPlus is a compatible plugin. Maybe your update encountered an interruption and that corrupts some of the ConvertPlus files.
Please completely delete the remains of your convertplus
folder from /wp-content/plugins
, then reinstall it from the Pro > Validation > Extensions area.
Remember to clear all your caching features (plugin, server-side, CDN, and browser’s cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Cheers!