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.
It’s worth noting that this post was from last month before they announced the usurious pricing of the API. However the fact that they were doing this does not bode well for people (like me) trying to avoid using their horrendous app.