‘XX’ violates the C++ One Definition Rule [-Wodr]

The full message is:

/home/path/to/my/file.h:45: avertissement : ‘XX’ violates the C++ One Definition Rule [-Wodr]
/home/path/to/build/Project_autogen/TT4UNRZD7V/../../../../../../Project/file.h:45:8: warning: ‘XX’ violates the C++ One Definition Rule [-Wodr]
   45 |   void XX();
      |        ^

/home/path/to/my/file.cpp:391:6: note: ‘XX’ was previously declared here
  391 | void Class::XX()
      |      ^

I think this is a false positive, but I would like to know if you have encountered this warning in your own code.