Hi There,
We have a problem with motion blur in 5.1.1
The animation of the bike is from Blender and exported as fbx. 
The camera is attached to the root bone of the bike and motion blur is set to 0.5 Shutter 1/60 , App 1.4, 27 mm.
The project settings are attached (Virtual Production preset)
We think it’s related to motion vectors, and/or import/export from Blender
Thank you in advance for your replies.
Piotr