If you have the class
class A {
public:
	A(const A&) = delete;
	A& operator=(const A&) = delete;
}

Doxygen will give these warnings with the default Doxyfile:
test.cpp:3: warning: Member A(const A &)=delete (function) of class A is not documented.
test.cpp:4: warning: Member operator=(const A &)=delete (function) of class A is not documented.

But in this case it is obvious that the functions are deleted and cannot be used, and thus don't require documentation.