Hi Henriette,
I'm sorry to hear about the navigation issues; this should not be happening! I'm happy to help troubleshoot.
We can start by checking if you're working on your local drive; working on a network drive can cause erratic behavior. If the problem still happens, try these steps to fix possible installation issues, then republish the course.
If these don't help, I'd be glad to look at the Storyline file to look at the triggers or rule out possible corrupt elements. You may also share it privately by sending it along in a support case. We'll delete it when we're done testing. Thanks, Henriette!