How to stop WorldSpace UI Rendering behind things it is on top of

I’m trying to have a menu rendered in World Space but for unknown reasons it renders BEHIND everything except the skybox!
The UI Canvas is not physically behind anything, it’s between the camera and the world geometry yet it renders behind all the world geometry

Please help, this doesn’t make any sense!

I just discovered the problem is caused by using the “Mask” component. When I deleted the Mask component the UI inside the main scrolling window now renders at the right depth, the issue no is that it’s not masked… so this isn’t really a solution, but it shows where the problem really is