‘wp’ action hook not firing in admin and login?

I just observed the same problem, and fixed it by using the “admin_init” Action instead. I only want it to fire in Admin, but if you want it to fire for Public as well as Admin, simply use two add_action’s, one for wp and admin_init, though I would make it conditional:

if ( is_admin() ) {
   add_action( 'admin_init',...
} else {
   add_action( 'wp',...
}