UE 5.5+ weird random material parameter interactions bug

[Rawalanche]

Hi,

I’ve recently migrated my project from 5.3 to 5.5 as I was hoping that after 4 hotfixes, 5.5 would finally be somewhat stable, but I started to observe some very weird behavior related to material parameters:

Unreal 5.4+ buggy shader compilation

I was trying to set up Vertex Animation blending but I just could not figure out why the normals from Vertex Animation B bleed into Vertex Animation A even if Vertex Animation A is completely disconnected. It looks like the new, rewritten 5.4+ shader compilation can somehow mix up material parameters even though they have unique names. Deleting the material parameters in completely disconnected section of the shader node network suddenly fixes the issue.

Has anyone came across this or similar problem, and knows the solution?

Thanks in advance.

[Rawalanche]

And as usually, I found a solution minutes after writing the post

If you ever run into this kind of issue, make sure you never blend multiple VertexInterpolators, but always use just one after the blending: