We have noticed that sometimes the tabs at the top of the course page disappear. It seems that sometimes, when you scroll down to the point where the tabs are off the top of the screen, they get "stuck" and do not re-appear when you scroll to the top. I have reproduced this on the Desktop app and on an Android phone. See the video below for a demonstration.

Steps to reproduce:

1. Go to a course page
2. Scroll up and down near the top of the page, far enough to make the tab bar slide out of view.
3. Scroll back to the top of the page. After some time, the tab bar disappears.

I haven't worked out the exact trigger for this behaviour. Once the bar is gone, there is no way to get it back apart from leaving the course and returning.