My UI is failing hard on resolution change

I’m having a great deal of difficulty getting UMG to work right.

My case is I have a game that I test in-editor. If I press a key it switches to iPhone XS Max propotions, and if I press it again it switches it iPad Pro 12.9" proportions, and after that toggles between them. The initial res is neither of these, but the default aspect ratio matches the iPhone. In both cases I add on 51 pixels for the title bar because I’m normally doing PIE (rather than standalone like in the screenshots below).

When I switch to the iPad aspect ratio it doesn’t change the scale of the UI correctly (maybe at all).

The logo and the content are actually two different widgets, so let’s focus on the logo for now. This is how it’s set up:

As you can see I’m just making the window taller and shorter and the UI scaling is going haywire. That white border box should fill the screen, not get smaller.

This is how I change res. I’m even invalidating the UI:

Everyone I’ve talked to has said that canvas is an abomination and to start with a border as my root widget, so I’ve done that. It fixed a couple of issues like the logo scaling completely wrong, but it still doesn’t scale the whole UI to fit the screen on res change. Neither did canvas.

What am I missing?