I saw this movie at a pre-screening followed by a Q&A with the Director and Producer of the movie.
 
What  a lot of people suspect here is 100% correct per the Directors and  Producers own admission. They changed Taylors first draft of the  script significantly, specifically the third act. In my opinion, this  definitely shows. The movie was not in line with Taylors other epic  screen plays, and it felt like the third act was completely missing.
If  I recall the details of the changes correctly (which btw they were very  proud of), they said Taylors original script had the third act  culminate with BDTs character searching out the cartel boss, and  continuing his rampage from the first movie. Instead, the Director  determined the focus should be on character development. So the focus  was shifted to BDTs relationship with the girls character, and they  completely rewrote the ending.
The  Director also did not see the relationship between JBs and BDTs  characters as a friendship. He wanted to have them face off and go head  to head in the movie instead of working together, resulting in the  strange way JBs character made the phone call to BDT to basically tell  him they are enemies now. They also apparently took out significant  storylines related to the terrorists, and instead resolved that  storyline by saying the terrorists were actually US citizens.
 
If  anyone has any leads, I would love to get a chance to read the original  script. I have faith that Taylors original ending was much true to the  story and the characters.