Alright solution found…
2 bugs happening at the same time.
1.) Dont use texture samplers within a material function if you want them to respond to work correctly with packed level actors and custom primitive data.
2.) The scalar parameter was bugged for choosing which texture array when not using custom primitive data. I had to create a new scalar parameter and permanently change the name of the parameter to be different then before. Thats the only way the material instance sees it. If i try to go back and name it the original name it will disappear again. So thats my work around…