Hi c0r37py,
it doesn’t seem you’re actually attaching your Hair to your head socket; the socket is specified as second argument in SetupAttachment (and if you shouldn’t need the “attachtocomponent” afterwards). Just try
Hair->SetupAttachment(GetMesh(), TEXT("headSocket"));
headSocket should be the name of your socket (and again, you do not need that attachToComponent afterwards – you’re already attaching your hair with setupattachment). Also, either you attach this in code or in the editor; looks like you’re prone to the former approach, and you’re doing it right with your UPROPERTY.
Hope that helps!
Cheers
f