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.
Mean there were times when I was logged out of Reddit and was trying looking up something on mobile and the constant badgering to install the app just had me tell it to flip off and I looked elsewhere instead. Lot of people tend to do things based on how convenient it is for them and if they go ahead with this, sure maybe some will download the app but a lot of other people will just get fed up and stop, particularly if they were using the browser version so they didn’t have to deal with the app in the first place.