Justice League is apparently undergoing extensive reshoots, according to the Splash Report. All movies like this go through reshoots, but the problem that the report is presenting is that these aren't the normal types of reshoots. These are reshoots similar to what happened to Rogue One: A Star Wars Story or Fantastic Four.
Now, we should clarify that this is a rumor coming from Splash Report — but they did break the Rogue One reshoots story, which ended up being true. Still, they could be wrong, but considering the timeline, it wouldn't be surprising if it wasn't wrong.
The timeline consideration is that Justice League went into production about four to six weeks after Batman v Superman: Dawn of Justice. We can assume that Warner Bros. had a detailed plan about how they were going to tackle the team-up movie now that the rest of the foundation is finally being rolled out.
Then Batman v Superman came out and got critically panned. This is the movie on which they planned to build their entire universe, and suddenly it was being called a disaster. While fans were kinder to it than critics, to say that they are divided would be an understatement. Suddenly, Warner Bros. was likely looking at their plan and having some serious second thoughts.
Jump forward to the present, and we have rumors coming now that the movie has been completely overhauled due to reshoots. When asked about the extent of the reshoots, Splash Reports' source replied with the word "significant".
Speaking on a condition of anonymity, they said that in the 17 months between the start of principal photography and the final cut arriving in theaters in November that the film will have essentially been "remade…twice."
That sounds bad, but we have to remember that reshoots are not all bad. While movies like Fantastic Four and even Suicide Squad feel like they were broken even further by their reshoots, we also have to come back to Rogue One. Those reshoots might have taken out an amazing scene in the run across the beach, but the final product turned out great, and there's no reason to assume doom and gloom when it comes to Justice League and its rumored reshoots.
The plan that WB/DC went in with before Batman v Superman is not the same one they walked into that production with, and we can only assume that it changed again after the response to Suicide Squad. The latter was a movie that felt hacked to the bone by an editor struggling to make a bunch of pieces fit together and mostly failing. There is every chance that WB/DC is doing these reshoots because they want to make sure they get it right this time.
Warner Bros need Justice League to be a massive hit now that King Arthur: Legend of the Sword is looking to be one of the big bombs of the summer, if not the year. Wonder Woman is tracking well, but not the kind of numbers to turn many heads considering it's looking to make the same at the box office as Doctor Strange. This is a project that will define the DCEU going forward even if Wonder Woman is a critical and financial smash hit. They can't afford to mess this up, and if they need to overhaul the entire movie to make that work? Well, you do what you have to do. The rest of us just want a good movie.