Storyline slide order doesn't match navigation pane

Hi all - I'm very green with Storyline and don't know what I'm doing wrong here. But when I preview my course the order of the slides on the navigation pane is not the correct order in how I've set them up in the course. I've confirmed all slides are numbered in the correct order and when I click play, they advance in the right order but the navigation on the left is off and so it looks like as slides advance the user is jumping all over the place, and also means the learner can't use the navigation accurately.

Any ideas on how to fix this would be greatly appreciated! Thanks.