When typing "todo" or any similar search term in a search engine, the first result that comes up is https://to-do.office.com. This page has a button that takes you to login, even if you're already logged in. It's necessary to enter your email before it seems to recognize it and finally bring you to https://to-do.live.com.
This might be a common problem across Microsoft web properties hosted on office.com, but one I notice particularly for To-Do as I don't tend to keep an open tab for it and rather close it / re-open it multiple times during the day.
