Morgan La Fay's hairdo noticeably changes from her long shots to her close-ups.
At one point Valiant goes through a door without a sword and emerges onto a battlement with one. After a brief fight he goes through another door with a sword to emerge without it.
Valiant relieves a soldier of his sword during a scuffle then seemingly throws it aside and runs off but the next shot of him following Linet up a stairway he has a sword again.
When Sir Gawain catches the arrow shot by Humphrey, he raises the hand that contains the end of the line upon which the arrow is traveling long before the arrow reaches the end.
When the Green Knight is addressing the revelers at the King's feast, after he has been decapitated and has put his head back on, his sleeve falls back when he raises his arm and you can see the line where the makeup applied to his hand ends.
When Sir Gawain aims his bow at a unicorn to hunt it, the horn which is strapped to the horse wobbles up and down as the horse moves its head.
Camera and sound equipment shadows fall across Gawain and the Baron during their sword fight in the pit.
In the final scene when Linet asks Gawain to touch her cheek before she leaves. The boom mic is visible at the bottom of the frame in the foreground and is hastily retracted as the scene progresses.