Reflections showing wave pattern after adding plane We actually it is quite hard to describe my problem with only using words.
1

My problem is this weird wavy contour. Without the plane underneath the can, the reflections look fine (like in the bottom part), but even when I use the standard Glossy BSDF on the can and a plane with Diffuse BSDF this problem occurs.
Using a higher roughness on the can doesn't change much except that the border between the black part and the correctly reflecting part becomes less prominent.
I am using two area lamps that are lighting every other object correctly.



In this I am using a HDR image for world lighting and a plane without any specific material and now the bottom part doesn't reflect like it should.

Also, the mesh isn't faulty or something in that particular place and if I look at the can from another angle the intersection moves.

I would like to know what I did wrong and I'd be glad for your help.
This is the proper reflection of a curved surface. the peaks of the wave pattern are actually just the corners of the plane.

you could reduce the effects by changing the camera angle or the size of the plane. maybe it helps adding walls and making the plane more of a rectangle than a perfect square.

And the reflections aren't wrong in your second image. the bottom part is just the reflection of the plane.