Storyline keeps changing my slide order

Part of the problem is that when slide order is changed, the order of the thumbnails is not changed until the next time they are redrawn. So the changing of the order of the slides, and your observing the results of that action can be widely separated.

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. 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.

Like Judy says, the menu is congruent with the actual order only occasionally, and that right after you follow her suggestion to rearrange it. Again, "Jump to [slide name]" can help that problem, too.