[UMG] The image under scalebox disappears when its alignment set to centre

I’m having a weird issue with UMG scale box:

I’ve created 2 blueprint widgets, one of them is the child widget and the other one is a main widget.
The child is referenced in the main widget.

The issue happens here. I use some umg scaleboxex in the main widget to hold the referenced child widget (the intention is to keep the child widget’s original width&height ratio). I set the child widget’s (which is under the scalebox) alignment to be either centered vertically&horizontally or fill vertically&horizontally, then populate the main UI widget to the level. When I play the level, only the ones with alignment set to be fill both way can be displayed, while the centred aligned child widgets cannot be seen at all. But, I need to use the centre alignment setting, otherwise the scalebox won’t work to keep the child widge’s original ratio.

Sorry if this has been posted before, but I haven’t been able to find any answer.
If this has already been asked, can anyone give a link for this?

And I am wondering how can I upload my project here