Factual error: In the first scene where Dr Strange is preparing for surgery he uses improper surgical gowning technique breaking aseptic protocols. Strange puts on a mask after washing his hands, contaminating his clean hands by bringing them in proximity to the non-sterile environment of his face. Surgical masks must be worn before the full washing of hands. Another error is that he inserted his hands all the way through his gown to don gloves. Hands must never leave the sleeves and gloves must be put on with the sleeves still covering.
Continuity mistake: Strange is at home, looking for help on a video chat, then throws a tantrum by throwing everything on the table to the floor. Christine enters with food, and the reverse shot shows all the items and computer back on the table.
Continuity mistake: When Hong Kong is being destroyed, a vendor's sign falls to the ground, written in English. However, in the shot where the city is being restored, the same sign is now in Chinese.
Other mistake: When he rushes a patient to brain surgery they show him and the other doctor operating without surgical masks. When they cut away and come back they're wearing masks. Also, the doctor that is assisting him is an ER doctor, that would never happen in real life.
Continuity mistake: The wound and blood on Strange's left eyebrow is first fresh, then dry, then it's gone, then is back again.