The scene where Haymitch reads Plutarch's letter to Katniss was originally scripted to be Plutarch (Philip Seymour Hoffman) talking to Katniss in person. Unfortunately Hoffman died before the scene was filmed.
The cast has said multiple times that the hardest scene to shoot was the sewer scene. It took three weeks to shoot and was physically challenging, and it was very hot on set since they shot on location in actual sewers.
Gwendoline Christie replaced actress Lily Rabe as the Commander Lyme character in the film. Rabe was forced to drop out due to a scheduling conflict with a previous commitment to perform in "Much Ado about Nothing" at Shakespeare in the Park.
In the epilogue, Josh Hutcherson (Peeta Mellark) wears a blonde wig for the first time. Hutcherson had dyed his hair blonde for all the Hunger Games movies and hated it a lot. Since the epilogue was shot months after principal shooting ended and the shooting only took a few days, Hutcherson decided not to dye his hair again and wore a wig instead.
Actress Meta Golding reprises her role as Enobaria, Victor of the 62nd Hunger Games. Her character previously appeared in The Hunger Games: Catching Fire (2013) as one of the victors in The 75th Hunger Games and Third Quarter Quell. In the plot, although her character did not appear in The Hunger Games: Mockingjay - Part 1 (2014), she was recovered by the Capitol after the Quarter Quell but was not present in the Capitol when District 13 went to rescue Peeta. In the book it is stated that because she was from a pro-Capitol district it was unlikely that she was ever held prisoner, unlike Johanna, Peeta and Annie.
The control consoles in the District 13 control center set were originally built for the Mission Control Center set in Apollo 13 (1995) and were later acquired by a prop rental house and rented for this movie. Several of those same consoles, still with badges reading "Panem" and "Property of Capitol District Defense Forces," were used in the Mercury Control Center set of Hidden Figures (2016).
According to Francis Lawrence, the film's first-cut running time was 2 hours and 51 minutes, but the final cut's running time is set to be 2 hours and 16 minutes, making it the third longest installment in the franchise.
The Carbine used by Boggs and the rest of the team escorting Katniss is the H&K G36C. This is a 5.56mm carbine used by the German Army and various Police units around the world. The receiver on the weapons in the film has selections for Safe, single shot, 3 round burst and fully auto.
In this film as well as the previous one in the franchise, Katniss only wears her hair in her signature braid when she appears as "The Mockingjay" for propaganda purposes. All other times she wears it down or in a low ponytail.
A crowd-pleasing moment at the end of the movie, that surprised even the filmmakers, is when Haymitch says goodbye to Effie Trinket by giving her a kiss on the lips. Woody Harrelson and Elizabeth Banks decided to do that unscripted.
The final scene of The Hunger Games: Mockingjay - Part 1 (2014), where Katniss wakes up and learns Peeta has been hijacked (after he tries to kill her) was originally intended to be the opening scene of this film, but during production, the filmmakers decided ending Part 1 after Peeta is knocked out by Boggs and the screen cuts to black was too big a cliffhanger for general audiences, so it was added after that instead.
When the victors are seated around the circular table, the bowl from the first The Hunger Games (2012) can be seen on the hutch behind Katniss. This was the bowl of nightlock berries for Seneca Crane's suicide.
The huge underground place Squad 451 enters through the middle of the movie is actually a real place in Japan. It is Metropolitan Area Outer Underground Discharge Channel, the world's largest underground flood water diversion facility, located between Showa in Tokyo and Kasukabe in Saitama prefecture.