It almost looks like the UV triangles of the square surface are not having the noise rendered on the line between them. Yet, the line is inverted from the default position, possibly (default would be bottom left to top right diagonal). Try deleting triangulation of the mesh faces to see if it corrects somehow.
When you bake a material in engine there’s not supposed to be any meshes in use that you can access or change.
Render material to render target particularly shouldn’t use meshes at all… in theory at least?
Details on setup here (I think, didn’t re-read it).
@op and @Arkiras
Does changing the resolution of the output produce different results?
It really does look like the result of a drawn line.
Could it be part of how Simplex works?
Meaning - someone boneheadedly replaced the texture in engine and this is therefore causing the effect?
Docs do state that Simplex cannot tile.
And the line is already visible in OPs noise before the Add. So maybe there’s that invovled…