I went back into my project and tested the issue again making sure to stretch the meshes. I was able to successfully reproduce the issue you are reporting and took the liberty of creating a bug report (UE-13213). Thank you for being patient while we test the issue on our end, and for the provided information needed to reproduce.
Just to clarify, the answer I provided before this one should have resolved the original issue you reported about seams on instanced static meshes. Since you are aware of the issue just reported, I would suggest not scaling Instanced Static Meshes non-uniformly until a fix is implemented.
If you have any other questions or need additional assistance, please do not hesitate to ask.
Thank you for creating a bug report and, in turn remaining patient with me.
Just to clarify, the original seams were also a result of the incorrect normals occurring due to non-uniform scaling. It’s just that when I posted the question, I hadn’t come to the conclusion that this was the problem.
Basically, this entire thread is just different manifestations of the same underlying problem.
I will avoid non-uniformly scaling instanced meshes for now, but if implemented, this will be a really powerful feature, allowing batched rendering of architecture (walls, panels, etc.) instead of just using it on foliage/props.
