I see...
So I tried to render your scene and it's as I suspected. There has been some subtle difference between VFB and PV for some time now, especially in darker tones. Normally, this is pretty negligible so we concentrated on fixing more serious bugs, but your scene is pretty dark, so the difference is bigger here. I'm afraid that we won't fix this as soon as you'd like, so my workaround suggestion would be to try to save the render and use whichever framebuffer shows the correct result for you.