Be sure and validate before you run. If it isn't shading it means it did not run to completion, which means the output cannot be added to the map.
If it really is not running as expected, clear things out by validating and saving the model and project, close Pro, open Pro, and see if it starts behaving. In my experience this OFTEN helps when things are just acting weird, the restart releases all file locks, clears memory of cruft, etc. and everything magically works again after the restart.