First thing I'd do is check the barrel nut. I've heard of some new guns having it very loose. Before doing so please read up here on properly removing the flash hider, if so equipped. You can either make your own barrel nut tool or buy one. Once again, all this has been discussed in the past & can be found by searching.
That brings up the question, did they possibly remove the flash hider already? If done improperly, that can screw up everything.
Also might want to check the ejector. If you search here, you will find discussion & pics on how it should be positioned. This can get bent out of position during cleaning if not careful... especially if using a bore snake. I put a straw over mine during cleaning.
Otherwise send back to S&W & they will take care of you.