Material instances not working on mobile

Hey there, I’ve recently started development on a mobile game, and currently I’m encountering a problem with material instances.
Whenever I use the parent material on an actor it seems to work fine. However when I use a material instance deriving from that parent it only shows the default material on a mobile preview.
Any Idea on why this is happening?
Thanks!

UPDATE: Apparently this problem only appears when I use the project launcher, if I package and install my game the material instances work fine.