Please note that when you switch themes then the widgets and menus in wordpress site gets reset .
This is not from theme and it is default behavior of wordpress.
So you need to set the widgets again for the front end dashboards .
refer :
https://wplms.io/support/knowledge-base/wplms-dashboards/
For the menus you have to set the menus again for the student instrcutors .
Make sure that Student and Instrcutor menus are enabled from wp-admin -> lms -> settings .
refer :
https://wplms.io/support/knowledge-base/student-and-instructor-specific-menus/
For the courses page please make sure that your wplms theme all its plugins and modern child theme are updated to latest .
Also make sure that you do not have any page or content with slug same as " course " .
Please delete that page and re-save permalinks again .