I have a scene with a couple of hundreds of quite simple objects copied onto points, however all of a sudden the scene stopped rendering properly. It takes forever to render with micropolygon/raytracing, but with PBR the scene renders just fine.

If I replace the geometry with spheres instead it renders fine in micropolygon/raytracing as well. So it seems to be some kind of geometry related issue. Any clues? Any setting I could try changing?

Are the objects running through the near clipping plane of the camera? This can cause mantra problems, or has in the past.

When in doubt reduce the problem. Cut the geo down to one instance, then double the numbers until it happens again.

Don't forget you can dump to IFD (turn off binary) and look through it for any weirdness.

The problem suddenly disappeared and it's now rendering fine. However if i returns I will give your suggestions a shot. Thanks.