With the new update, all the pages' content slides "under" the HEADER and cuts off the first two inches of content.
This is a known issue.
You may temporarily fix this issue by using a small widget, as described here: https://forums.adobe.com/thread/2374391
Or you may sign up into the Muse Prerelease Program (www.adobeprerelease.com) and instal a very stable prerelease version. This version installs alongside to the public Muse version and won’t interfere with it.