I see this a lot, so I'm going to leave this here... Mods duplicating assets (such as shaders/textures) and the reason is because for some misterious reason, they dont get loaded on certain games/computers/people/whatever, if you just reference them, as you would normally do. I don't get why, and because I'm not really publishing, I never really digged into a fix for this, until that is, I shared it with a friend. What fixed for me:
On your mod's engine INI add the packages as FreeSeekPackage, like this:
Now, I'm unsure which type of packages should be added, UPKs containing Assets or the Archetypes (like Firaxis, I'm taking the best practice of keeping different UPKs for Archetypes and Assets, and so should you), when I tested with my friend I included both package types and it fixed for him, but I strongly suspect you only need to add packages that contain assets, makes more sense. And this way not only you optimize the game by avoiding to load the same texture more than once, but you are also able to trim your mod's size by A LOT! This is specially true to mods that use the same textures as the ones already included in the game.
OBVIOUSLY, this only applies to assets that have no edits whatsoever. If you're editing just the Diffuse map, but keeping the Normal/Multimask ones, its pointless to duplicate them! Just keep the old reference and add the UPKs as SeekFreePackage and it should prevent you from getting missing textures/assets