I encountered this issue after creating a custom animation blueprint for spinning the wheels of a vehicle relative to its velocity. The render used 66 temporal samples for what should be excellent motion blur quality, causing the wheels to spin 66 times faster than they’re supposed to and causing awful motion blur artifacts.
I found a workaround that works perfectly for my case. The bone velocity > vector length is divided by the radius of the wheel to get the spinning speed. So to compensate for the temporal samples, I now multiply the radius with the sample amount first. To make it easier to adapt it to different settings, I made it a float variable that is Instance Editable and Exposed to Cinematics so I can edit it directly from the sequencer.
I don’t know how to apply the same solution to your cases, but the universal idea is to essentially divide whatever variable decides what speed things are going at with your chosen amount of temporal samples.
I’m on 5.3 to be clear. No clue if this is fixed in 5.4 or 5.5.