To reproduce:
1. Open attached project
2. Create a new Sprite Animation asset (Assets >> Create >> Sprite Animation)
3. Click on the new Sprite Animation asset and lock inspector
4. Find a collection of sprites to add to the animation under Art/Characters/Circle/Attack
5. Select all sprites in the Attack directory and drag them into the Frames array in the Sprite Animation inspector window.
6. Notice that the frames are added in a seemingly random order -- not the order that they appear in in the project hierarchy window.