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.
In a weird way, they probably are - I guess they figure that users who don’t see any/many ads are not contributing to Reddit’s finances, while still causing Reddit costs in terms of bandwidth, etc. In which case it makes sense to get rid of them (a bit like having an email database with 100000 people on it, but only 5000 of them ever open the emails - if you have to pay more to store those 95000 who don’t, then it makes some sense to rid of them.)
Problem is, how many of those who view on old or on 3PAs are the ones making/sharing the content that brings eyes to their ads in the first place - maybe they’ve analysed it and decided that the loss of goodwill and incoming content from those people is more than offset by the savings to be made in having a smaller but more captive audience?
They might be right - but I hope not, because they’ve acted like dicks.