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.
https://web.archive.org/save/https%3A%2F%2Fold.reddit.com%2Fr%2Fhelp%2Fcomments%2F135tly1%2Fhelpdid_reddit_just_destroy_mobile_browser_access%2Fjim40zg%2F
Stop spreading lies, Reddit is already doing a lot of bullshit you don’t have to make stuff up to make them look bad.
It's not lies, that's certainly been the case for me. If I visit old reddit, I get a broken page. If I log in and then visit old reddit, it works.
Maybe they're doing a google and rolling out the change gradually across different regions.