Particle SubUV expression does not use texture input.
ParticleSubUV function in Material Editor do not take Texture from Tex node.
Since int32 UMaterialExpressionParticleSubUV::Compile(class FMaterialCompiler* Compiler, int32 OutputIndex) in MaterialExpressions.cpp do not have process for Tex input (`TextureObject.Expression`) that its parent class have.
Is Particle SubUV intended not to use Texture input? then I believe Tex pin need to be hidden.
Result: Particle SubUV does not accept Texture from Tex input. Connecting Particle SubUV output to main material node results in Error message "Missing ParticleSubUV input texture"
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-51813 in the post.