Which is something he's done before. It's like bringing in Tarentino to do a dialogue polish (ever seen Crimson Tide? Who do you think wrote in the pop culture references?) or that time Lucas hired Spielberg to work on the pre-vis for Anankin/Obi Wan fight in RotS.
It's not a sign the movie is in trouble, it's a sign they want to make sure it gets the best attention it deserves. Believe me, if things are even half as bad as some insist on then the studio wouldn't be bringing in a specialist to help the director, they'd be firing his arse and getting a replacement in ASAP and as I said, he wouldn't be allowed anywhere near their press events. Much less
showing up dressed as a Stormtrooper to someone else's Q&A. These are not the actions of a troubled production. It's just what happens when a production is so good at keeping a lid on things, the clickbaiters will just start making it up.