Storyline keeps changing my slide order

The first thing to check is that the slides actually have changed positions, and not just moved around in the story view pane. The true order is the way your learners view them when published (or your view in preview). What you see in the story view pane is not related to the actual order.

I have found that when I click on a slide thumbnail in the Story View that if the mouse makes even the slightest twitch during the click, it will modify the slide order, even if I don't see it. Changing one trigger can drastically affect the story view. Sometimes you make a change, and it takes a while for the story view to redraw the thumbnails.

After what seems like years of wasted time spent trying to find where slides are and how they got moved, I have determined it is a vast saving of time to create every "jump to ..." trigger using the slide name, rather than "Next". That prevents the slides from ever changing sequence. They may change numbers, but not order. A simple drag will change their numbers back.