Motion blur disappearing when rendering sequence

[pjkw]

I have a problem where the motion blur of my liquid is coming and going.
When I render one frame its always there, it also seems to be there on the first frame when rendering a sequence.
But as soon as I render a sequence beyond the first frame it disappears. It doesn't matter what frame it is, the same frame can first be rendered with motionblur when just rendering one frame at the time, and then without motionblur if its part of a sequence.
The only thing Im changing between the renders is the frame range.
Im using 3.99 beta on max 2019 with vray next update 2.1

Edit:
Seems its related to the fact that Im adding modifiers on top of the fluid, relax, displace modifiers, FFD box (space warp). And actually it seems to be happening randomly when I just render one frame at the time too. One thing that stands out is that when the motion blur disappears and the render is done, the mesh has disappeared in the viewport, changing the frame brings it back.

[Svetlin.Nikolov]

Hey, we're gonna try to reproduce the issue here right after we cross off some urgent tasks. Do you have a scene which produces the issue or do you know which of these modifiers might be to blame? If not, we'll try different mesh modes and all of these mods to see if we can break it here as well...

[slavina.nikolova]

Hey, we've reproduced it. Thanks for letting us know about the problem! We will add it as an issue in our system.
We will update the thread when we have something on that.

Thank you,

[pjkw]

Cool, any workaround or specific modifiers to avoid? I ended up using motion blur with vectors in AE but would have been nice to have real motionblur.

[georgi.zhekov]

It seems to be happening with most of the modifiers - so the safest bet would be to export the mesh to alembic and then use the modifier on top of it. You can check how to do this in here - https://docs.chaosgroup.com/display/...s-AbcVelExport

Cheers,