ScrollRect contents do not align to top until input received

Consider the following image:

When I first start my game and open this menu, the contents of the scroll rect do not fill to the top unless there are more items in the list than the container can show at once.

When I provide input to it though (for instance scrolling via mousewheel), the problem is resolved for the duration of the game when using this menu.

I add the items in a script, but I do not think that should have any bearing, as I am using layout components.

Any idea what I could be doing wrong based on this image?