After the tower explodes, a group of office workers rushes to the elevator to get down but they get stuck inside the elevator and suffocated and died from smoke. Why didn't they take the stairs which would've increased their chances for survival.
Why wasn't the UVX tower up to code with having sprinkler system installed, buildings today are required to be up to safety code, also why didn't the maintenance workers follow the safety rules and shut off the power earlier when the power consumption jumped up, also when the furnace room exploded why didn't they have a fire extinguisher on hand which could've prevented the fire from spreading.
In the opening of the movie, when the building woman inspector is inspecting the building, she is pushed to her death by Eric Steele and Lucas Beaumont. The police would've found the woman's dead body in the elevator shaft, and would've arrested both Eric and Lucas and charged them for murder. It's unknown why the police didn't send in a search party. Since they finally discovered her body near the end of the film.
While Ben and Anne were trapped in the elevator. Why didn't they both stay put on the elevator and have Paul bring down all the elevators sooner. They could've got out of the building faster and more safely.