Why might a render scatter around rendering as opposed to center-out rendering?

Support Lighting and Rendering
1

Hi,
Usually when I render something it appears to render from inside to outside, as in the checkered boxes start at the center and over the course of a few minutes (or a few hours) work themselves to the edges. The render finishes as the corners are rendered.
Today though blender is doing something different: instead of working from inside to outside, the “rendering boxes” are going randomly around all over my scene rendering randomly.
Why might this be happening?

EXAMPLE:

Screenshot at 2017-05-29 16:40:53.png1920×1080 256 KB


This is just curiosity, blender is still rendering fine.
Thanks,
~Lich

2

Show us a screenshot with your “Performance” panel visible. Might be Hilbert spiral now selected?

3

Happens a lot when there are tiles that need significantly longer to render then others and while the renderer is still keeping to it’s center -> edges pattern it simpy looks less organized.

Also Hilbert Spiral (http://bl.ocks.org/nitaku/bffd66a05d5bf04aefa7) goes from center to edges on larger scale but tends to do some seemingly unorganized things in between.