I have a pretty stable and fast enough internet connection, so I rule this out.
I use Firefox 63.0 on a Ubuntu machine.
When I click "$x$ questions with new activity" and the $x$ happens to be some integer in the $30$s or higher it takes really long until the new questions are displayed.
Now when I click just "Questions" on the left it loads in an instant.
Does this maybe have something to do with the fact that I display 50 questions per page?