Weird edge problems when using retainer box

Hi !
I am creating some 3D interactable interface for my project. To create some rounded corner boxes for my buttons I use retainer boxes on which I apply an effect material.

The problem is that the retainer boxes behave weirdly when I move away from them. As you can see on the attached pictures, the edges do some weird stuff.

274998-fromafar.png

.

I initially thought it was because of my material but the problem remains even when I remove the material as can be seen here. !

275001-no-mat.png

Any idea what I can do to solve the issue and keep my edges crisps? I really don’t want to go back using images for this (it’s both a dirty way and poorly scalable)

PS: for better comprehension, here is my widget BP: