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.
They’ve already made the “new” reddit web view unusable for any sub marked NSFW. I feel sorry for the web devs at Reddit that spent all this time making a responsive site that works on mobile, then to be forced to artificially block access to push app usage.