how does UI/Canvas Draw order work?

Ok, here’s my setup
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The blue menu with the white border, is the entireity of StatsPanelCanvas.
What i want is for it to always draw BEHIND StatsButton, which is just below it in the child list.

As far as i understand, child objects are drawn in their order, so the last child should always be on top of everything, and the first should always be underneath everything. But that’s not so, if i move the stats button down:
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Ok so clearly i must be wrong, lets try moving StatsButton above the StatsPanelCanvas

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That works, great! .
Let’s start play mode now, and see it in action.
During playmode, the StatsPanelCanvas gets moved around and transformed a lot.
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So what’s going on here then?

But if i now, while still in play mode, swap their order again;
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I have no idea what is going on here. Someone please explain this to me. How can i make the stats button ALWAYS be on top?

Hi, I have exactly the same problem (U 5.4.1f1 Personal) now and I cannot figured out why neither object ordering nor override sorting ordering does not work as I expected. Has anyone found a solution?