May and I tried to probe a bit more to understand whether it's a
cultural thing (e.g. maybe the hamburger icon is only recognisable in
North America/Western Europe).
I did not even know that the icon at the top left of mobile site[1] had a name, but it took me a while to figure out it was clickable, and I always forget I should click it when I want to log in. It is as far from intuitive as possible for me. But then, I am from Eastern Europe, so hamburgers and their icons are not part of my culture.