When using the FireFly engine at the following settings, I get some error artifacts on what I think are bucket boundaries.

Use displacement maps on
Minimum displacement bound 0
Raytracing on
Case Shadows on
Smooth polygons on
Remove backfacing polygons off
Use texture filtering off
Minimum shading rate .5
Maximum texture resolution 4096
Pixel samples 6
Bucket size 32
Raytrace bounces 4
Post filter size 4
Post filter type sinc

The object pictured is a 1-sided square (the front side obviously:) with a pretty simple material and a few lights. The rest of the scene is quite complicated (22.7M compressed).

Earlier in this project (the first big one since upgrading to P5) I had the Pixel Samples set to the max (12) and kept getting crashes during renders. Through trial and error I found I had to keep that setting lower to prevent the crash. I assume that if the max setting didn't crash, it would produce better subpixel antialiasing on bucket boundaries.

Thoughts?

Thoughts? Yes ;) Either use the HiRes square or connect a math node to displacement and set it to something like 0.001. That should help getting rid of those strange whatever :)

For a start, I'd recommend simply setting the displacement bounds to 1.0 - that might fix it.

Doesn't setting displacement bounds to 1 mean that any displacement higher than 1 will get clipped, resulting in a hole? BTW, I haven't tried replacing the 1-sided square with a HiRes square, but I doubt it would help the problem, because today I noticed the same bucket edge rendering bug on a V3 body part, which probably has a lot more vertices than the square, and it has some bump on the skin, so it's not totally flat. This really looks more like a subpixel render bug when rendering on one edge of the current bucket (the 32x32 (or whatever) area being rendered). It might help if I could turn the pixel samples up to 12, but that crashes me on lots of different documents.