When you export all artboards to a single page and the artboards seem to be out of order check the artboard order.
The way you can order them is to open the layers panel. You can show the artboards list by double clicking the artboard or clicking the name of the artboard.
In the project above the order the artboards will be displayed in the order:
- Intro
- Whiskers
- Mittens
- Snowball
- Ending