Expression Controls in mogrt files work in AE, but not in Premiere

I'm trying to create a mogrt Template for the first time, following this tutorial: https://www.youtube.com/watch?v=JOoAq_xnviw. Everything works fine in After Effects, but when I export it as a mogrt and import in Premiere, none of the properties that I set up via expression controls works, only those that I directly pulled from the layer into the Essential Graphics window.

So when I have a shape layer, go into Content > Rectangle > Fill and drag that colour into the Essential Graphics window, I am able to change the colour in Premiere too. But when I put a "Fill" effect on the layer, as told in the tutorial, and pick whip that colour onto a "Color Control" Effect on a Null layer – I can change the colour via the Essential Graphics tab in After Effects just fine, but Premiere just ignores this. The Colour Control property is shown in Premiere, but the Shape will have the regular rectangle fill colour, not the one determined by the Fill effect, and while I am technically able to open the colour picker via the Colour Control in Premiere, it just doesn't change colour no mater what I pick.

Now I chould just do the first method without expression controls, but it doesn't work with every property I want to set up, so I'd really like to figure out what I'm doing wrong with the null layer.