Audio problem: In the opening scene, Bond sees Tracy in the ocean and drives his Aston Martin onto the beach to rescue her. When he stops, we hear screeching tyres, but he is driving on sand.
Revealing mistake: When Bond throws a Blofeld henchman off a cliff near Piz Gloria in the Alps you can see that it is a dummy as it's arm swings round and wraps around the whole dummy.
Audio problem: In the scene where Irma Bunt has seen the girls off in the village and starts chasing Bond and Tracy, tire screeching can be heard from her black Mercedes. As it is driving on snow, such a sound is not possible.
Audio problem: In the scene where Bond and Tracy are in the car race on ice, Tracy is heard to say "James, how do we get out?" but her lips don't move at all in the accompanying close-up.
Continuity mistake: When Tracy is battling that balding guard during the climax, she finishes him off by pulling him into a metal patterned wall in a way that ends up with one of the circular sections on his head like a crown. When he falls down the stairs this circular section disappears.
Audio problem: In the sequence of a party in Portugal, when Bond runs to Tracy to apologise after saying something unpleasant about her, he grabs her and starts talking with his back to the camera. His facial muscles don't move - the scene was later dubbed.
Continuity mistake: When Tracy and Bond are talking in the casino, and Bond tells her to stay on 5, she has her left hand resting against her chin. As she says "people who want to stay alive play it safe" she moves her hand down to the table, but then when the camera cuts back to Bond the reverse shot of her shows her hand still by her chin, and then she moves it down again.
Continuity mistake: In the scene where Bond is getting out of Draco's car to visit Gumbold, his tie is neatly within his jacket. He bends over to speak to Draco, and the tie is dangling out of his jacket. In the next shot, he straightens up, and the tie is once again neatly within his jacket.
Continuity mistake: At the start of the scene where Bond is helping with the assault on Piz Gloria, look at Tracy's hand just after the bald guard presses it down on the object to disarm her. You can see blood, but a couple of minutes later when she kills him there is no blood to be seen.
Continuity mistake: After Bond saved Tracy from drowning (at the start of the movie), he is fighting with the two men of Blofeld. In the first shot they're standing about 5 feet from the waterline (on the beach), in the next shot they're waist deep in the ocean.
Plot hole: Blofeld tells Bond that he realised he was not the real Sir Hilary Bray when Bond told him that the Bleuchamp tombs are in the Augsburg Cathedral. Blofeld informs Bond that they are in-fact in the Saint Anna Kirche, and the real Sir Hilary Bray would've known this. However Bond had gotten his information about the Bleuchamp tombs in Augsburg from the real Sir Hilary Bray earlier in the film.
Continuity mistake: When Bond is fighting the villain on the beach in the pre-credits sequence, the two fight in the sea and Bond's hair gets wet in the process. But when Bond says "This never happened to the other fellow" his hair now appears to be completely dry.
Continuity mistake: When Bond and Che are fighting, Che knocks out one of the white wooden bars behind Bond. However, in the next shot, two bars are missing on the upper half of the wooden structure, one on the bottom half. Seconds later, just before Bond throws Che into it, the bottom half of the structure is complete again, and only one bar is missing on the upper half.
Visible crew/equipment: When Bond is being chased on skis, he flies over a ridge and through some trees, landing very close to the edge of a cliff. A cable is clearly visible tied to his right ankle to keep him from going over the edge.
Plot hole: Blofeld is played by Telly Savalas. In a previous film, Blofeld had met James Bond and had ordered him killed, yet in OHMSS, when Blofeld meets James Bond, he doesn't recognise him. It's well established over the course of the Bond movies until the reboot with Casino Royale that they all take place in one timeframe, so they should have recognised each other.
Other mistake: As the assault on Piz Gloria begins and the helicopters approach the facility, on the right of the screen one seems to be hovering near the helipad as another passes behind it. The helicopter in front fades to a slightly different position as the one passing it disappears and reappears several meters ahead. On the left of the screen the third helicopter appears out of thin air. (This was obviously caused by a dissolve effect, but since the sound effects are constant there doesn't seem to be any indication that a visible edit or time shift was intended for this scene, so it's a mistake).