We need to see your .blend file, and maybe a better statement of “what, exactly, is your question?”
No, I did not mean in Blender, but in real life. Here are the pictures that I have found on Google Images:
(See the upper right corner)
Waiting for someone to discover this phenomenon when rendering in Cycles and, not understanding the effect, files a bug report.
Once Cycles gets MNEE (and path guiding later on), we will probably get more inquiries as to whether Cycles is misbehaving (because most here have probably not spent a lot of time studying the physics of light).
My wild guess is that it’s an anisotropic effect where the light has more spread diagonally, due to the tiling.
I am not sure if that pattern only appears when the glass surface have a certain pattern, but on one such glass I see small rectangular protrusions. If I create that kind of pattern on a surface in Blender and render with CyclesX, will a light source behind that surface would show such pattern?