Pink material when using 2 x PBR (Principled BSDF) materials into a mix shader w/Eevee When I combine two PBR materials (with Principled BSDF Shaders) in Eevee through a Mix Shader, the output is pink?

Alone, each Principled Shader works, even if I pass one material through the mix shader, that works. As soon as two go through, it's pink?
I've tried re-creating in a fresh scene with two Principled Shaders, some basic noise textures for color/roughness/normals, but unable to recreate in that case. Seems to be linked to the use of images possibly?
Any help is most appreciated. Thanks!
Have tried the materials on their own, and they work fine:

Top Principled BSDF Shader works fine on it's own:



Bottom Principled BSDF Shader works fine on it's own:



Running a single BSDF Shader through the Mix Shader works as expected



The mask I am using (for context):
I believe the limit for EEVEE is 24 textures per material. In cycles, you can get around the limitation by enabling &quot;open shading language&quot;, but I think in eevee, you're stuck. In the end, it doesn't matter what the &quot;theoretical&quot; limit is - If you hit a point where adding a new texture to the graph causes it all to turn pink, you just have to find some other way around it, such as using a texture atlas.