Looks like more than a 1/4", so you can't use a Caddy RLC, you will need to use an extender like an Arlington BE1 or Raco add-a-depth ring. Raco's are a bit spooky but easier to install.

Because of the mud you will probably have to remove bottom screw before you can wiggle the top out.

NEC 314.20 Flush-Mounted Installations. Installations within or behind a surface of concrete, tile, gypsum, plaster, or other noncombustible material, including boxes employing a flush-type cover or faceplate, shall be made so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (1∕4 in.).

Installations within a surface of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall extend to the finished surface or project therefrom.