There is a pressure on sequels that can never be present during the first instalment of a franchise. The pressure to be equal or better than the first movie. The pressure to live up to the expectations based on the success of the first movie. Deadpool 2 had to follow up Deadpool, be better and funnier, and that is a lot of pressure. Even for a comic book character, who is able to break the 4th wall and survive pretty much everything. And sometimes that pressure becomes too much.