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.
Honestly I’m tired of every website trying to annoy or force me to download an app. Mobile web design is perfectly capable of doing the vast majority of the functionality you get with an app. It’s all about gaining greater access to your device’s functionality and data.
If someone told me you’d be expected to install a separate piece of software on your device for each website you frequently visit back in 2010 I’d have said that sounds like a stupid idea and it’d never catch on.