As quoted from the linked post.
It looks like you’re part of one of our experiments. The logged-in mobile web experience is currently unavailable for a portion of users. To access the site you can log on via desktop, the mobile apps, or wait for the experiment to conclude.
This is separate from the API issue. This will actually BLOCK you from even viewing reddit on your phone without using the official app.
Archive.org link in case the post is removed.
Actually, it wouldn’t surprise me if they decided to kill it sooner rather than later. Restricting mobile access even further indicates to me that they’re probably trying to get all their negative press out of the way as quickly as possible.