Widgets Rendering Out of Order - Text Element Ignoring ZOrder At Runtime (5.4.1)

Got a weird one here. Basically I have a Widget Blueprint for all my HUD elements, one of which is a big black Image that covers everything which I use for fading in and out. The ZOrder for this is set to 999, all other elements the ZOrder is either 1 or 0. In the Widget Blueprint editor, the image correctly covers all the other UI elements, but for some reason when I run the game it covers everything except one specific text element. The text element itself doesn’t seem to have a ZOrder setting, but the button it’s attached to has its ZOrder set to 0. Even more bizarrely, if I duplicate this button, the original button is hidden correctly, but the new duplicate one is broken!

This is looking like it might just be a bug with Unreal (5.4.1) at this point, but is there anything else that might be controlling the layering of this element?