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.
I know that twitter pulled a lot of the same bullshit but I have to give them and their developers credit: they created a great app that ensured people could move away from their preferred 3rd party app pretty easily.
I will only use Friefox with ublock origin to browse Twitter on my Android. I planned on doing the same with old.reddit come July 1st, but it sounds like reddit has other plans.