I've done a lot of research, but it looks like all of my findings relate to Storyline 1.
Hope there is an update and a quick fix in Storyline 2.
Slide numbers can be helpful for several reasons: Slide Number.
Slide numbers are easy to add, but they can be frustrating, as well. In this tip, I’ll show you how to insert page numbers and also give you some troubleshooting techniques.
To make changes that will affect all of a presentation's slides, use the slide master.