(at around 1h 35 mins) Near the end of the ritual, the heart monitor of one character goes into a flat-line (asystole). The character of Ann, who is a nurse, uses a defibrillator on that person. No medical professional would ever do that, administering a shock to asystole is useless.
(at around 24 mins) When Angela is reading the poem "Jabberwocky", the last line is misquoted. Instead of the correct word galumphing, Angela said galloping.
(at around 1h 3 mins) The demon in this movie, according to the credits, is Lamashtu, therefore, when it sees Chris McNeil, the "We've met before" quote is factually wrong since Chris met Pazuzu instead. However, Lamashtu was considered to be the wife of Pazuzu in ancient Mesopotamian mythology. This makes it not so much a "goof" as a clever reference to Pazuzu who, while depicted as Lamashtu's husband, was also the entity who opposed her extreme malevolence. In myth and legend, where you find one, you find the other.
(at around 58 mins) When asked by Victor why she didn't witness the exorcism, Chris respond with: "My opinion? Because I'm not a member of the damn patriarchy." Given everything that happened and what she did experience, it's very unlikely she would genuinely feel that way.