The crash occurs consistently and for sure is related to avatar's hair. I've replaced the avatar with others to which, in CC4, I attached the same hair, yes, it's crashing. If I'm replacing the hair with another one, there's no crash. Crash doesn't seem to be related with the MP4 encoder - app crash no matter if I use hardware/software encoder. Also, crash doesn't seem to be related with a particular last frame - no matter how long I set the timeline, IC crash at the last frame. It might be related with a particular rendering - light or physics - condition in the project, since the same avatar used in other projects doesn't make IC to crash. I don't think it's hair related, though, since I used the same avatar+hair in other IC8 projects without problems. Also, I got the same crash with different avatars and hairs.

I simplified a crashing project as much as possible and I replaced the avatar with CC4' native Camilla, to which I attached the same troubling hair - see the download link below. Just open it IC8 and go straight to render as video - tadaam, crash. I hope will crash so you can catch the issue.

https://www.dropbox.com/s/yg70875ectnj9ur/crash_on_video_render_last_frame.zip?dl=0

P.S I reported this issue initially on the forum, seems the issue also hit other users:
https://forum.reallusion.com/513732/MP4-rendering-consistent-crash-at-saving