Maybe A Bug From Engine?

i don’t exctualy say that is a bug , I Create A ChildClass From UStaitcMesh , And Some Error like : error LNK2001: unresolved external symbol “public: virtual bool __cdecl UStaticMesh::StreamOut(int)” (?StreamOut@UStaticMesh@@UEAA_NH@Z)
i override some Functions disappear those error,but some function in the parent UStaticMesh is with the word “final” : virtual bool StreamIn(int32 NewMipCount, bool bHighPrio) final override; i can not override it ,why it doesn’t work .wish someone help ,thanks.