I'm not sure that CC3 recalculates normals, but I could be wrong. I notice that when I send in an OBJ accessory, it will retain unsmoothed normals (as an example), requiring a manual fix either in Blender or within Character Creator.
As to your solution (clearing Custom Split Normals Data), it didn't work for me. It still causes a crash. Also, I've been importing as an OBJ. I hope that information assists in your search for the technical dilemma.

Btw, the accessories export function seems to trigger the OBJ export by default. In fact, if I try to set it to FBX, it will add an .OBJ extension to the end of it.

I think I figured out the issue. When the plugin triggers the exporter, it uses the FBX exporter, but only gives you the option to save it as an OBJ. This doesn't corrupt the file, but it makes it impossible to import. Unless you manually change it back an FBX, then it will work. I hope that helps you.

That's a big whups on my part. It uses the same extention as the character file imported. So if you imported an .obj file it would name the accesory export as .obj, and then it completely ignores that and exports it as an fbx, with the wrong extension.

I've changed it so that it exports it as an .obj for .obj characters and .fbx for .fbx characters.

https://github.com/soupday/cc3_blender_tools/releases

It seems to work great now, thanks for the fix!

Does this not suport cycles? 

I'm getting strange bugs when I use cycles. Sometimes eyelashes come in solid, sometimes they don't, and hair almost always looks off
here is just importing the FBX (skin land eyes ooks way off, but the hair looks fine)



and here is the same model, but using the CC3 importer

the hair is all chunky? and the shadows are messed up, speifically the bangs

Also, for some reason I'm getting "Seams" along differenct textures? They are even visible in the workbench rneder (See the highlight on his forhead) 



I am using 2.93

Try turning off the Smart hair, Eevee highlights and fake bump in the add-on preferences.
These settings are largely geared towards Eevee and the hair will behave more like the direct import for Cycles.



Also make sure you have enough transparency bounces (50+) in the Render Properties (Cycles) / Light Paths / Max Bounces settings. Otherwise you will get bad shadowing effects.

Nice, some very well deserved recognition in here:



https://www.youtube.com/watch?v=ycpdB8kHZJw

Indeed!

RAG DOLL COLLISION ANIMATIONS FOR ICLONE 8 & 7
---------------------------------------------------------------------------------------------------------------------

Ghost Origins

My latest Feature length film created with Iclone.

My Sci- Fi Graphic Novel on Amazon: https://a.co/d/9k3cwoY

My IMDB listing
Anabran Abdhul Quarnain - IMDb

I may need a drink. :)

Or two.

I tryed to import a character to blender with this and copied all shader settings from the body to my clothing object to try replicate digital human shader perfectly onto my cloth object. Is this possible somehow?
When i exported back to CC3 my whole character was white and all materials missing. I tryed mimic the Digital Human shader with SSS with almost perfect results, i'm looking for perfect results.

Import a character to blender seems to work like a charm. Is there any specific way you should do it when exporting changes out from blender back to CC3 again? If possible.
I have a very limited experience and understanding of how all these softwares and such works.

Thanks!