When implementing cpp code into cpp imnplementation source file.
If using namespace brackets-enclosed namespace (not using "using namespace" )
Such as :
myclass.cpp : 
//...
namespace $[ns]{
///...
    everythings within this $[ns] and any sublevels brackets-enclosed namespace are ignored. cpp-code assistant,  any method implementation, etc, are hidden. Showing only unrelated [global] symbols.
}

Does happens only into cpp source files using brackets-enclosed namespace.