Artefact in imported Hair I have wierd bump in hair and i am desperate. 

I created a model in VRoid then exported it to blender. Then made clothes and details, exported the whole thing to MMD. In MMD it worked okayish.
After that i wanted to render motion in blender with fancy lighting and physics. Here's where I faced problems. Exporting back to blender using add-on caused problem with hair - physics had a defect and hair followed after head partly. And also has this weird bump artifact.



Add-on makes automatic mash/bones/weights from MMD, therefore there was a problem. I deleted all hair physics, so next desision was to make new rigid bodies. Still I was met with the same problem. This bump..thing is still there. After 1st rigid body in chain the rest follows the head. The 2nd rigid body follows only partially. Weights and normales are okay, baking all physics doesn't solve it. I would gladly appreciate help

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Paranted:
Apologies as I'm kind of new, so I'm unsure how to fix all of your issues, but I assume the bump is an issue with colliders, as a similar thing happened with one of my models.
Try editing the collider for the head by moving it or making it smaller. This should at least partially help with the weird hair lump. I removed the hair in my screenshot to make it more easily visible, but this specific collider seems to give a lot of issues if you go directly to blender.