After adding the block "Main menu" and setting it to "Display throughout the entire site" all activities added to courses will not appear inside the respective course but somewhere else ... likely on the "Site home" or within the "Main menu" block.

Steps to reproduce:

• Login with administrative privileges
• Goto "site home"
• click cogwheel --> "turn editing on"
• Add a block --> Main Menu
• click cogwheel within Main menu --> "configure main menu block
• Select "Display throughout the entire site" from "Page contexts" --> save changes
• Create a course and proceed to course content
• Add an activity or ressource (doesn't matter what kind of I suppose)
• After filling the mandantory fields and clicking "Save and return to course" you will not find the just-created activity where you would expect it to be but somewhere else ... likely on the "Site home" or within the "Main menu" block.