This happens to me pretty often. For example, right now I have the debugger stopped at a breakpoint in a method . . . and it isn\'t displaying any variable values at all.
I have been stuck a while with this problem and finally find out a solution. I think that many reason can causes this bug but in my case here is the solution. While you are in the breakpoint position check the included classes. I was including using double quote a file which was located using include path.
#include "MyClass.h"
instead of
#include <MyPorject/MyClasses/MyClass.h>
So if you have this problem try to double check your inclusion and import. I know it seems weird but worked for me and I have been able to reproduce it by putting back the Double-Quote include.