After updating Moodle from 4.0.3 to 4.0.4 we received the follow notification while using Boost theme

" Call to a member function remove() on bool"

We use:

• Courseformat: single activity
• Activity: SCORM

When we go to the course as site admin we don't receive a notification. 

When we turn debuggin on we see the following :

Uitzondering (EXCEPTION) - Call to a member function remove() on bool
Debug info:
Error code: generalexceptionmessage
Stack trace:

    line 1030 of /lib/classes/navigation/views/secondary.php: Error thrown
    line 220 of /lib/classes/navigation/views/secondary.php: call to core\navigation\views\secondary->load_single_activity_course_navigation()
    line 881 of /lib/pagelib.php: call to core\navigation\views\secondary->initialise()
    line 953 of /lib/pagelib.php: call to moodle_page->magic_get_secondarynav()
    line 71 of /theme/boost/layout/drawers.php: call to moodle_page->__get()
    line 1473 of /lib/outputrenderers.php: call to include()
    line 1399 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
    line 146 of /mod/scorm/view.php: call to core_renderer->header()

When we switch to Classic theme students can enter the course and do the activity.