There was nothing huge, but there were several issues that occurred that, when put together, make the production sound worse than it was.
- The movie had roughly 5 months of pre-production without a full-time director since J.J. was busy finishing Star Trek Into Darkness.
- It was determined that the biggest returning character couldn't appear much in the movie or he would detract from the new ones.
- The original writer was let go after over a year of work and less than a year before principal photography.
- The film got delayed six months because it wasn't going to make it's original intended May 2015 release date.
- The writing process was so rushed that the shooting script wasn't completed until several days after principal photography started.
- One of the stars broke his leg on set when a door fell on him and the director hurt himself trying to lift the door.
- The shoot had to go on a two-week hiatus because of this during which time the relationship between two of the leads was rewritten. Originally, Rey knew right away that Finn was an ex-stormtrooper and was distrustful of him because of this. The scenes between them were rewritten and reshot so that Rey didn't know about his past and was friendly with him from the get-go.
- J.J. and the editors kept tinkering with the film during the entire post-production process. There wasn't really a locked cut until November of 2015. John Williams, who had recorded the scores for the previous Star Wars movies in about 3 weeks each, recorded for months on The Force Awakens because the timings and sequences of scenes were constantly changing.
None of these are that unusual. Many movies hit several of these types of problems. Writers being switched out before filming begins is nearly bog-standard for blockbusters, as is a director not being there for the entirety of pre-production. And I think we've all become aware of how often blockbusters have reshoots these days. But there were no huge reshoots like in Rogue One or changing of directors during the main shoot like Solo, or death of an important actress like The Rise of Skywalker.