Hello Ciao Valentijn, I hope you are doing well today!
If I understood you correct, when you navigate from your admin dashboard to CoursePress > Assesment you can’t see the assessments, right?
Do you see any errors? Would you please deactivate all other plugins and try again? If everything is well, activate one plugin at a time to find the one that causes this conflict.
If this is not a conflict with another plugin, please enable WordPress debugging. Place the following in the wp-config.php file:
define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );
Try to access the CoursePress > Assesment menu. This way all errors will be saved in the debug.log file inside the /wp-content/ directory. Let us know the errors you see inside.
Cheers,
Nastia