This is a “normal” behavior of figma that makes no sense. It happens when a parent container that has scroll contains child items with shadow effects applied to them.

Steps to reproduce:

1. In design mode (img 1) I created an auto layout that is 24px in X coordinate. It stretches until the end of the device frame, has scroll set to horizontal and contains 3 squares with 36px blur shadows. Horizontal position and autolayout alignment is set to the left.
2. In prototype mode (img 2), the start position is the same as the design mode.
3. Unfortunately, if I scroll to the end and back again, the child containers are now 36px further from the left edge.

Final consideration:

Yes, I'm aware that I can apply the shadow to the parent container, but that's a workaround and not a fix - Its not everytime that I can do that, since this problem also happens when the whole frame is set to overflow.