why do shapes vanish when on a box

when I place a shape on a box it vanishes completely now and then when rotating

I know there is z-fighting which can be seen when a rectangle is on a rectangle but wouldn't expect it to vanish completely. Tried to do grouping to fix it but doesn't seem to make a difference.

see simple demo I created here, thanks.

https://codepen.io/coder787/pen/MWJbJQo