Thanks a lot for your reply, Vako!
I guess it could be a bit hard to share access as the website is not live yet and I run it locally on my laptop (using WordPress Studio). Do you think it would still be possible to access it with this plugin? If so, I will arrange it tomorrow when I’m back at my workplace again.
I found out that it could be connected to the search icon, when I deactivate this icon, the warning disappears and the menu bar looks normal again.
I guess this is something that should be solved in the theme. As probably more people want to use the search icon and use Translatepress at the same time.