Hi @Ghos79,
I see that your viewport is set to Medium scalability. Does this problem disappear when you switch to High/Epic scalability?
Some material features, such as distance fields, are not available at the lower scalability settings by default and can break materials.
I would also recommend updating your graphics drivers just to rule that out as a cause.
Additionally, does this issue persist if you replace any textures with basic colors? There is an engine bug on I believe 5.3-5.5 that can cause your textures to go black and need resaved.