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.
Morgan La Fay's hairdo noticeably changes from her long shots to her close-ups.
Camera and sound equipment shadows fall across Gawain and the Baron during their sword fight in the pit.
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.