This is a weird one. The Preface for the SCAG now displays the Credits page instead of the preface in the book. The urls are both still correct, so it's not a redirect error. The change must have just happened recently, because I had looked at it just two weeks ago and it showed correctly. The Preface for the book in the DDB app is correct.

 I can confirm this bug by following the link to the preface: https://www.dndbeyond.com/sources/scag/preface

Confirm that this is not working for me either
It's especially annoying since the MAP of the region is in the preface, 

And viewing the map on the app has terrible resolution 

Yeah. It seems like a relatively simple edit to fix the problem? Compared to other parts of the site anyway.

Well, I just purchased and downloaded it today and the preface is missing on the mobile app version but not here online. My app version shows the credits where the preface should be. Also, I was able to purchase this in a discounted bundle deal here online but the mobile app shows none of the bundles or sale prices. 😕

Yes, I just discovered the same this morning. I was looking for the full Sword Coast map which is in the Preface of the SCAG.  But in my downloaded version in mobile, I can't get to the Preface. It goes to the Credits when I try to view Preface. I really wanted to pull up that map.

Is this going to be fixed for mobile? I really wanted to pull up that fuller Sword Coast map thats available in the Preface.

Just ordered the guide and on my iPad and iPhone apps the preface directs to the credits page it works on my laptop browser but not iOS apps