Hi Scott,
We've identified the issue with the login screen as a bug that was introduced in last night's update. We are working on a fix that will be deployed tonight. I apologize for the trouble.
Regarding your other question about bookmarks and sections: I'm working on a GeoNet blog post on this, but that is expected due to a change we made in how sequential sections are implemented in this beta release. You can no longer have two sequential sections in a row. If you made a story like this in beta 1 or if you create this situation, for example by deleting or moving an immersive section, sequential sections will be combined.
In your case, you also lost a bookmark since the sequential section that had the bookmark was combined with a previous section when you opened builder for the first time after the update. I'd recommend inserting a title section to break up your story and you can add a new bookmark on the new title section or on the new sequential section following the title section. Sorry that this change has affected your story.
Owen
Owen Evans
Lead Product Engineer | StoryMaps