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.
Yeah. There are a ridiculous amount of users that just use the official app and don’t really care about 3PAs or the whole API situation.
It’s a shame. I remember the old Reddit before all the redesign and other crap they added.