It's a bit more than Chic bun medium hair problem.
Yes, that hair physics for one reason or another is troubling, but it is a consequence of internal error from more deeper issue.
If you disable physics for Real_Hair, the project renders fine. So it is a physics issue.
But I believe at this point the real problem is animation layer. It causes a permanent hair damage within the project.
And it appears Real_Hair is just most vulnerable to such a damage.
Replacing hair with the same Chic bun medium does not fix the issue.
Removing animation does not fix the issue.
But this does:
Save that motion with collect clip as Motion+
Delete the clip along with Transform key so that she is standing in T-pose at 0,0,0
Apply saved Motion+ clip
Reapply "Chic bun medium" from Shared Template\Hair\Style
Render. All should render fine.
So at which point the hair physics is getting messed up is for the RL to figure.
Another reason I am saying it is not the hair problem (at least not directly), because my project is old and there is no modern hair on any of the characters there and not even any DHS.
Yet it crashes just the same. I need to investigate the issue there.