Many times, like at 1:04:32, the message "no network signal" is seen on the phone screen, but the signal meter has plenty of signal level.
The Isolation Ward is repeatedly mentioned as being on the 7th floor of the hospital. But the hospital shown only has 5 floors.
At one point, the main character uses an automatic defibrillator to shock a door handle after analysing heart rhythm. Most operating theaters would have their own defibrillators with ECG and controls, not a simple one as shown in the film. Secondly, it should not shock without a shock-able rhythm - which a door knob would not have.
The entire time Madison Taylor is hooked to her IV bag, the drip monitor never drips and the level of saline in the bag never changes.
When Bruce Willis is interviewing Madison in her hospital room, you can hear an EKG machine slowly beeping in the background even though there are no leads connected to her.
During the final scenes, Madison runs with her sister and enters the elevator, but one of the corrupt cops enters the lift too. She had a gun on her at that time, but decides to run off again instead of shooting the guy.
She is taken to the seventh floor of the hospital, but the long shots of the hospital only show five floors.