Unfortunately, even while testing under various conditions and speeds the issue wasn’t prevalent enough at low “per object size” values. I had a discussion with the developers and a fix for this currently isn’t on the roadmap.
That’s why I recommended voting on the issue because the settings/situations used to reproduce these artifacts in an obvious way are considered “unreasonable or extreme”. A high vote count shows that a lot of people disagree with this decision and are getting problems with motion blur.
If the community shows more interest in the quality of motion blur and it’s issues things like this are more likely to be addressed.
Sadly, other than log the bug and argue a case there isn’t much else I can do to overturn a developer decision.
Regarding the other issues you mentioned, if you haven’t already, please make another Answer Hub post so we can address those problems individually.
While this article mostly relates to feature requests it still applies to issues that we simply don’t have the manpower to address at this time.
https://headcrash.industries/stories/why-your-idea-might-not-make-it-into-ue4/