Variable sliders not working in AI

This is my first attempt at designing a 3-axis variable font (weight, width, height). I’ve been running into issues when I try to test the exported ttf in Illustrator 2021. Prior to the current version, the sliders worked after export, but “interfered” with each other, such as the width slider changing the weight in unexpected ways. Now, after seemingly correcting the masters, none of the sliders work at all, and only display the Regular instance. Here’s a stripped-down copy of the file with just the instances for H.

If axes interfere then you have a bad master arrangement. All masters need to be in a strickt rectangular arrangement.

I thought my masters were arranged correctly, but I’m not exactly sure what “rectangular” means in this case. Here is a visualization of how I have the masters arranged.

Is there a master in the middle? That is not arranged rectangular.

Yes, I wanted to have a master for the regular weight/width/height to have more control over those outlines. How should I incorporate that master?

Right now you need to add a master at each side of that cube.

I have an idea how I maybe be able to improve this but I’m not sure if it will work. And when I will manage to implement it.

Ah ok, thanks for your help!