First rendering: just a standard render on a workstation. Second rendering the same (still open) scene as backburner rendering on the same workstation.
I suspect volumetric because changes are along the border of a VolumeMtl box. Are there any known issues? Would like to know before digging deeper.
Good Luck
I would suspect UHD Cache if you are using it, although it looks a bit strange. Can you try the same with PT+PT?
btw, next time it would be better to upload 2 separate images so that we can compare them easier. 
PT+PT results in similar different renderings. Diff attached.
Looks like the environment is different (which is plain Corona sun+sky). But how the …
I mean: same box, same scene just interactive session vs. BB single frame… strange.
Next test will be using no volumetrics at all, let´s see.
Good Luck
Wait a second…
Local Rendering standard
just a standard render on a workstation
just interactive session vs. BB single frame… strange.
So is this regular or interactive??
Results may differ between IR and regular - different GIvsAA is used, probably different UHD Cache settings, and the difference will be strong if you are using AO in the scene.
“Interactive” meant not Interactive rendering but interactive user session, meaning sitting in front of the workstation 
No differences using no volumetrics and no windows. Getting closer.
Good Luck
Moved this to the bugtracker, giving up.
Good Luck
I just realized that there is another similar case in our support. Only one texture on only one PC is getting “darker” during BB rendering. But we don’t yet know why this is happening…
If you can isolate the problem like this you are fine - the cause is somehow that specific box. I tested the above scene with 3 different workstations with same results. I assume it´s very difficult to debug such a phenomenon. And I would not touch it until 1.4 is out and dry
Feel free to test, it´s #0001844
Good Luck
duplicate of mantis case
