When Neagle & Ustinov are scrambling up a snow bank in order to light the beacon for the aircraft, they scramble up the SAME bank twice.
When Peter Churchill is being flown back to France, he takes off in a Mk1 Halifax B, but over the drop zone he's in a Mk2. This may seem esoteric, but the Mk1 had in-line Rolls Royce Merlin engines, triangular fins and a nose turret similar to the Lancaster. The Mk2 had Bristol Hercules radial engines, square fins and a blunt nose with no gun turret, a radically different aircraft.
At 43:39 when the equipment drop occurs, the instruction was to light the fires along the line of the wind but they are clearly aligned across the wing line.
The car used by the Germans to take Odette to the Americans is right hand drive.
Allied planes are shown with various dates in 1945 showing the Allied advance across Europe, however they have invasion stripes on the wings of the planes. These stripes were only used from D-Day until late in 1944; no Allied planes were using them in 1945.
When Odette and Churchill meet at the police station there is a tracking shot where the camera shadow is quite noticeable.