To reproduce this bug:

1. Open the attached project
2. Open ScrollView scene
2. Expand the Canvas/Window/Content/ScrollView/Content
3. Notice Content having Horizontal Layout group
4. Set spacing to some value ( for example 200 )
5.At design time, the grid works correctly, the objects are spaced
6.Play
7.At runtime the child objects all rest to the corner with a position of 0,0

More Notes:
If I disable the Horizontal Layout Grid, the children do not reset their position on play.
If I remove / add objects to the container the size of the container does not change
The size of the container should reflect its children
If I disable then reenable the Layout Grid, it works.