I'm using Blender 2.79 to render an animation. While many frames look consistent, every three or four frames, a series of frames crop up where a surface is rendered differently than the rest, often with what appears to be a depth of field blur in a different place. See the differences frame by frame with the ground surface here:
The first image is correct and the rest not correct.
I'm using a camera with a cube as a depth of field focus object, if that matters. Also using denoising, which doesn't seem to be the issue, and the fracture modifier for destruction. There is only one light in the scene that does not move.
Any hope for making the frames more consistent?