Please have a look at the ultra simple scene attached.

Motion Blur is enabled in the Redshift ROP, the spinning object has a trail node to add some large velocity vectors, the obj-level container has Velocity Blur enabled... but when doing a RedShift rendering, no Motion Blur in sight. The same scene with Mantra clearly show motion blur.

I must be missing something really really simple, like a typical gotcha... what is it?

Kind regards, Manu

I tested your scene and "mesh deformation blur from velocity attribute" was disabled, if you enable it, it works.
But you can use the standard motion blur (without the trail node), you just need to insert "$FF*10" instead of "$F*10" into the transform node to let houdini evaluate subframes.
Also put a normal node before the transform sop otherwise the cubes look weird but it's because normals make them appear blurred.

Thank you @madrenderman,

such small things once you know them (and remember them) and yet so time-consuming if you don't!

I'll try and remember next time!

Thank you again!

Kind regards, Manu

I am still super confused. I had similar problems, but even if I download the scene from "manu3d" and activate "mesh deformation blur from velocity attribute" I still don't get any motion blur... This is driving me insane.

Try this file, if you hit render you should see the motion blur. No need to activate velocity motion blur on the geo node