Visible crew/equipment: When Xander and Yelena are in the restaurant and they are shown through the window from outside you can see the reflection of a film crew member in the window. (01:04:35)
Revealing mistake: The Senator's Corvette explodes before it hits the ground. (00:09:10)
Revealing mistake: Xander has a XXX tattoo on the back of his neck. There are several scenes where you get a clear shot of the back of the stunt double's neck and there's no tattoo at all. Most noticeably in the scenes during the attack on the cocaine farm. (00:23:05)
Factual error: Xander puts a load of those sticky bombs on a line of motorbikes outside the bad guy's house. These bombs had a detonator switch, which Xander has. When he eventually sets them off, the motorbikes blow up in the order that he put the bombs on. These bombs didn't have timers or anything on them, so why would they blow up one by one and not all at the same time? (01:09:50 - 01:20:30)
Continuity mistake: When XXX is snowboarding down the mountain in front of the avalanche his goggles change from round to rectangular back to round again. The snowboard also changes repeatedly - from red to blue - throughout the entire run. The tops and bottoms of the boards - when high or low angles are shown - are different for both boards, so you see 4 different colors.
Continuity mistake: When XXX steals the Corvette, we see he breaks one of the side view mirrors. On the following shot we can quickly see that one side view mirror is broken and the other one is not. Then when XXX starts talking we see that both mirrors are broken. (00:06:25)
Continuity mistake: When Xander throws grenades to make an avalanche he unzips his coat. He fixes his goggles and jumps. In next scene his coat is already zipped up. Clearly he didn't have time to zip it. (01:29:30)
Continuity mistake: When XXX has to take the second test, after he runs out of the shack where the insane guy is, he finds a dirt bike. The dirt bike changes colours 3 times. (00:23:50)
Continuity mistake: When Ahab is launched, and XXX and Yelena are running, Yelena's singlet top changes from blue, to white, then back to blue again in different shots.
Factual error: In the very beginning, where the first agent gets killed, the Russian guy that shoots him says, "Zaraza" which means "bastard" in Russian. The subtitles say "I see him." (00:02:00)
Continuity mistake: When Triple X is brought to the diner, he has no jacket on. Later on in the plane, he's got a jacket on. When he's on that farm, the jacket is gone again, but when the raid is going on, he has got his jacket back. I don't know where he's always hiding his jacket, but it must be a really clever place to hide it. (00:12:30 - 00:22:30)
Factual error: When XXX is chatting with the CIA agent sent with the package, the agent mentions that he graduated MIT 'summa cum laude'. This is impossible, as MIT does not award academic honors to graduates. (00:43:10)
Revealing mistake: After X has put the bandaid explosives onto the motorbikes out the front of the compound, and is making an escape, he removes the bandaid off his bike and does a large jump over the castle wall. One of the bad guys is chasing him on another bike, and jumps the wall like X. As he is "flying" through the air, his long black trench coat remains hanging straight down. It should be flailing out behind him from his motion and the wind. (01:20:20)
Continuity mistake: When X ejects the roof of the car towards the end of the scene, you can see that there are no windows attached, however, after the roof is ejected, the windows of the car disappear. (01:46:00)
Revealing mistake: When Xander is standing on Ahab he is going about 80 miles per hour - that would make it like going through very strong winds. Yet he has no trouble standing on Ahab and the wind has no effect on him or his clothes. (01:48:05)
Factual error: The name of the sub is AHAB, but it's written ANAB, the "H" in Russian looks like a "X." (01:39:30)
Continuity mistake: When XXX arrives at Yorgi's mansion, there are girls in the water fountain out front. If you watch Yorgi's large bodyguard, the one that sports 5 or so earrings and a large beard, you will notice that he takes a girl out of the fountain. A split second later the shot changes onto XXX and in the background the large bodyguard is seen taking the same girl out of the fountain again. (00:54:55)
Factual error: When Ahab is entering Prague on the river, an aerial shot shows it passing Palackého Square and the Slovanech Cloister, which would mean that it's coming from the South. Yet in the final approach to the bridge when XXX is riding it, it's coming in from the North, with the hill at Letenske Sady in the background. This is all a moot point anyway, since the Vltava river has at least 3 small, man-made falls along its path through Prague, complete with intricate and time-consuming lock systems for river traffic, so unless the Ahab could fly there was no way it could even get anywhere close to town.
Continuity mistake: When Xander is snowboarding down the mountain to take out the communications tower, there is one point where the avalanche clearly bumps Xander and moves him ahead by about 12 feet. It appears to be a correction in the graphics so that it doesn't appear that the avalanche will outrun him down the mountain, however, poorly edited.
Visible crew/equipment: In the fifth shot of the amazing bridge stunt, an Arriflex camera with yellow cords hanging down from the camera is visible, off to the left of the screen. Also, in the same shot at the beginning of this shot (in the upper lefthand corner) you can see a guiding ramp setting the car to go off the bridge.
Answer: Vin Diesel chose to reject the sequel as he was being offered three different franchises, based on XXX, The Fast and the Furious concept and the character of Riddick (from Pitch Black) - he presumably felt that he couldn't commit to them all. In the end, he chose to go with the Riddick films and reject the others. The sequel is called XXX for the simple reason that the character is still present - they've just recast the role.