It's 2024 and I'm still having this problem! Has anyone found a fix? In these two examples, I both rendered the scene and took a High Resolution screenshot... the screenshot came out much better than the render

And you’re an expert user. That is truly puzzling. I thought maybe it was just some setting that I couldn’t find, some tick box, but since you are also experiencing it then that honestly makes me feel better.

Yet RL continues to advertise, market and hyper push their software in an Unreal Engine pipeline.
After 15 years of this BS I can say that I've had enough!

Yeah , I am having the same issue with smart hair :

Interestingly, I've actually seen that video, but it doesn't address the issue with hair cards, which is what the CC4/iC8 hair is. Using a groom asset, I don't experience the same issues.

Here's what I found:

https://www.youtube.com/watch?v=6AiUrL9Pa0s

I was not able to figure it out at all. I moved on to using Groom assets; initially created in Blender and then exported as Alembic files and imported into UE5. 

I may try again in the future with another character, but I couldn't figure out how to make it work in UE5. 

Did you figure out which lighting and/or engine scalability settings will fix the issue? Because I really want to use this hairstyle and I'm not having any luck tweaking things. I did take a look at the opacity maps in Photoshop. The Eyelashes (which look fine in both the viewport and renders) = 4096 x 4096; the Hair = 2048 x 2048; the Brows = 1024 x 1024  

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I don't believe that the thumbnails are entirely indicative of the way the material should look in the viewport. Lighting and Engine Scalability settings play a bigger part in how the materials will look.