Weird neck problem only with female Nords

[RG4327]

Now, I've always noticed this but never really bothered to do something about it. I used to cover it up with a scarf or longer hair etc.

 

The thing is, this always prevented me from making a short haired Nord as you would then see this "bulge" or "gap" at the neck.

I don't use any real body mod apart from this one:

https://www.nexusmods.com/skyrimspecialedition/mods/8505

I am using the vanilla option.

 

Besides, this was a problem before I even found this mod.

 

 

Can anyone tell me how to fix this or even what the problem might be?