From 4:26 until 4:29, Brooke is shown with a tattoo in her neck (Vanessa Hudgens's real tattoo), in later scenes it is gone.
When Sir Cole is first transported to modern day, a group of young women circle him in order to take a selfie. When the selfie is viewed on the phone, the girls are in a different order. When the view returns to the group, they are still in the original arrangement, not the one seen on the phone.
When Cole says "innermost weakness," he turns to look at Brooke. The camera changes from her side to his side, and now he's facing forward.
After Sir Cole has changed into modern clothes, he sits on the couch and invites Brooke to binge-watch TV with him. When the scene cuts to later in the evening and the two are still on the couch, Cole is back wearing his old tan blouse and gray sweatpants from an earlier scene.
When Cole and Brooke are Christmas Tree shopping he talks of adoring his Christmas Tree with candles and fruit . Christmas Trees weren't introduced to England until the 19th century, and Cole is from the 14th century.
When Brooke drives her vehicle in the snowstorm towards an unsuspecting Sir Cole, it shows her windshield with no snow on it. A minute later it shows the windshield completely covered by snow and slush. This is an unlikely series of events considering the "blizzard" going on outside.
At 5.24 minutes in the movie the knight meets an old woman and says hello. The word hello was introduced in 1827, where as the scene is from 1334. So by that time the hello word was not introduced.
At 27:33 into the film, Sir Cole opens the door for Brooke and her sister. When the door is open at its fullest, you can see green grass and trees, even though the film is set in winter.
Sir Cole shows up in 2019 Ohio from 1334 Norwich. The problem is that he would be speaking Middle English, while she would be a native speaker of 21st century American English. The two languages, while related, would be mutually unintelligible without considerable exposure or training.
When Sir Cole sees Brooke with the red dress he says she looks "positively radiant". The word radiant was introduced around 1600, no way he could have known it in the 1300s.
Sir Cole refers to getting an orange for Christmas. Oranges weren't introduced in England until the late 15th century, so there is no way that Cole would have received one in the early 14th century.
At the beginning a castle is shown and it has large windows with glasses. Glasses at the windows started to be used in Venice in the last years of 1400. No way they could be there in 1334. Before they were used only in churches.
The grocery shopping scene takes place in a Giant Tiger store. This franchise only exists within Canada and would not be seen in Ohio where the movie is set.
Brooke orders two cheeseburgers for her and Sir Cole but the burgers clearly do not have any cheese on them.