So, I tested a few different methods with your project that did not fix the solution yet. I pushed your project to a Note 4, Nvidia Shield and a . The enemy sprites did not show up for either of those devices either.
Could you please try and hook up a feature level switch node to your masked unlit sprite and see if the enemy sprites are working on your side?
[Utility Expressions - Documentation][1]
Utility Material Expressions in Unreal Engine | Unreal Engine 5.1 Documentation