From your video it looks to me like the graphic elemnets layer is behind the background layer, and the background layer is filled with opaque objects that block visibility.
Can you check the following?
Click on Graphic Elements, go to flyout menu "Layer Options."
Make sure that "Show Layer" is checked On.
Layers turned on, tried arranging sending to front. Happens in a new document aswell.
Can you share the file?
You have a white rectangle that covers the whole page on your B parent page, on the top layer. Delete it and you will be able to see the red background.
Layers turned on, tried arranging sending to front.
Object > Arrange > Bring to Front works on objects within a layer, it does not impact the layer order. In Windows > Layer, drag the graphics layer up to change the order.
It looks like you still have some issues with what is on which layer and what is in front of other things.
Content is stacked according to the layer on which it placed, and the order in which the layers are stacked. Content on Parent pages is always behind content added on a document page on any given layer.