For years I've been using Motion Vectors multipass from Cinema4d and using RSMB in aftereffects.
I know you need to remove the black from the motionpass (Just add luma key and set threshold on 1, most simple way ever).
This has worked perfectly for years untill R20 and now also R21, I cant get motion vectors working!
Every frame of my animation has full motion blur! It is not reading the motion info in a right way. I'm running RSMB 6 pro.