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.
That’s okay, kinda a fresh start for the rest of us who do migrate! It’s an evolution process and we are adapting and so hopefully reap the benefits of quality content and real interactions!