GLFW simple event handler
I see one major issue:

static std::vector&lt;std::function&lt;void(GLFWwindow*, int, int)&gt;&gt; resizeEventCallbacks;


You should never put a static variable declaration like that in a header. That will cause every file that includes the header to have a local copy of that variable. What you probably want is to put that declaration in the .cpp file so that it is local to that file only. The resizeEventCallbacks is an implementation detail that should be known only to eventmanager.cpp functions.