Not sure if bug or not but sometimes after stopping a render involving a Vray Denoiser render element + Lens FX, the effectsResult pass doesn’t show the denoised result unless I start fiddling with the Lens FX settings like turning on/off bloom or glare etc.
Might be related to the way you cancel.
Post effects will be updated when you press stop in the max render window.
When you press cancel the render is canceled and no post effects will be calculated.
Esc = Cancel and the “stop” button in the VFB is also cancel. 
Fair assumption but this happens even if I stop it well into the rendering, like 5-6 minutes in. And in that time I’m seeing vray applying denoising on the image multiple times.
Can you make a video? And are you sure you are stopping the render and not cancelling it like Ihno said?
I will try to next time.
Not sure. Why would this matter if the image was denoised before I stopped rendering? Shouldn’t I be able to access the last denoised result no matter how I cancelled it?
Ok, it just happened again and I recorded it. See attached below. I canceled the rendering with the red “Stop” Button in VFB.
vfb_effectsResult_problem.zip (1.39 MB)
I wasn’t able to reproduce the issue shown in the attached video. Would you send a scene to support@chaosgroup.com to check things out?