Couple of styling issue

For hiding excerpts field use this custom css:

.single-course .course_description h6 {
display: none;
}

@lupjoo: On your webpages I am able to see header clearly and nothing like your screenshots. Try clearing the browser cache. For instructors profile I would need the credentials to check.

The profile cover image is for p3 layout and p4 layout. The menu becomes invisible because there is no background there. When you change the layout it will be visible.

1) The course grid is misaligned because in some you don't have feature images and some course has very long name. So it will take its own space and adjust accordingly. For example, refer: http://prntscr.com/a4bdq6 The extra information will take its own space and adjust accordingly. 2) Its a theme feature that it display less info and when the user hovers over the info then it shows full info. If you want to disable it then use this custom css in your wp-admin->appearance->customize->custom css:

.archive.author .about_instructor .instructor_bio {
overflow: visible;
}

  Also I noticed your menu is not visble its full white, if you want to change it then you can change it from wp-admin->appearance->customize->body: refer: http://prntscr.com/a4bfvi

Please use this custom css to hide excerpt field:

.single-course .course_title h6 {
display: none;
}