According to Birth. Movies. Death. a source has informed them that Christopher McQuarrie was called in to "save" Rogue One: A Star Wars Story. This corroborates a Latino Review story from last year which also made this claim.
Rogue One was originally scripted by Gary Whitta, but when Whitta moved on to another project Chris Weitz joined the project, stating that "there’s a very strong structure from Gary’s work and that’s a huge advantage". It seems that not all went well, as sources claim that McQuarrie was brought in for at least two weeks to troubleshoot problems with the script and get the film back on track.
McQuarrie was previously called in to fix zombie outbreak adaptation World War Z and was also involved in bringing Edge of Tomorrow to where it needed to be.
Rogue One is said to be a military focused heist movie about a group of Rebels attempting to steal the plans for the Empire's ultimate weapon, the Death Star. The film is scheduled for release on 16th December 2016.