I have reported this to asobo through Zendesk, I hope they fix it in the next SDK update.
Try using projected mesh to add those textures above the lines.
I tried this with a default ProjectedMesh just to test it, tried all possible "Draw before" configurations and i was unable to Draw it above in-game PaintedLine.
The solution would be to draw the lines and the marks all in the same ProjectedMesh buut...
I have been thinking a lot about using ProjectedMesh versus custom Apron Textures and custom PaintedLines and... I'm not sure at all about what to choose.
Custom Apron and PaintedLines gives me lot of chances for merge between aprons, use decals and opacity in-game, in adittion i can control better PBR textures. And i have more control to make changes but it have the limitation that im talking about in this post.
In the other hand, using
ProjectedMesh could be a good option to pack all together into a mesh and could work very well on big airports since you have "all in one" but all the work has to be done previously on that mesh, as far as i know, we arent able to use decals above a projectedmesh or blend an apron above it (tell me if im wrong). Of course all this could be achieved using a combination of software like blender, illsutrator and substance painter but i should think about the exact workflow.
For example, if i use vertices over the mesh to draw the lines and marks of the taxiway/apron, im using a bunch of Vertices doing the airport less FPS friendly than if I simply use textures. Other option is paint directly on the mesh in Substance Painter but i have to figure out how to know where exactly to paint above that mesh since i can't see the aerial image under the mesh like in blender.
Well these are my thoughts, let me know what you think about it.
By the moment I'm sticking with Custom Apron and PaintedLines since i have all my ground textures almost done, but maybe on my next project i will change my workflow, I hope i will have a better idea in the future to choose the correct decision.
PD. Sorry about my english, Spanish guy here.