Motion blur causing dramatic shift in shadow and lightness of material

[stevesideas]

I've nailed it down to motion blur causing strange shifts in how shadows fall. It literally shifts from darker to lighter within 1 frame. Very noticeable. Any reason for this? Live project so any help asap would be appreciated.

Using max 2020 and Vray 5: Hotfix2 5.00.05 build 00001

[stevesideas]

It seems to be where the shadows are turned off for the floor/walls. It is confusing vray motion blur. Is this fixable or a known bug?

Basically the scene is setup with a chamfered cylinder acting as the floor and walls. It's a studio shot (mostly white). I've turned off the cast shadows and visible to reflections for this object to allow for the vraydomelight to act as the reflective source.

[Joelaff]

Do your lights have any key frames on them? Maybe they are spinning 360deg between two frames such that you can’t talk in the viewport. Curve editor would show this zoomed in.

Could be the shadow casting or receiving objects too. Check for weird between frame motion.

[stevesideas]

No keyframes. It's all to do with the shadows being off for that object and the motion blur. Vray doesn't seem to like that. I've basically worked around it by turning on casting shadows for the object and then increasing the multiplier for the light.

[Joelaff]

Can you post a simple scene? That is really interesting. I know I turn off shadows a lot for things like surrounding cyc walls. Not sure I have seen this.