Revealing mistake: During the night surfing scene notice that the sun is evident in the background (look closely it does not appear long). There are also shots where you can see clouds and faint blue sky. Moments later you see Keanu and Lori sitting in the water with completely different lighting which was actually taken at night and further distinguishes that the surfing shots were not actually done at night time. I heard the scene was shot during the day with a filter so it looked like it was shot at night.
Other mistake: In the fight scene where Bohdi helps special agent Utah you see that his surf board gets broken in two and then after the fight he is seen leaving without the board, but in the scene where he and Tyler are woken up early to go surf right before Tyler says "you look like you just saw a ghost" you see him carrying the same board.
Continuity mistake: During the scene where Utah is chasing the ex-president, we see Ronald Reagan run out of a house and scale a fence into a neighbours garden, instead of running down the driveway. The next shot then shows Utah running out of the house with the fence coming into view, but without seeing the ex-president, and then give chase over the fence. He wouldn't have known to jump over the fence, because he wouldn't have seen him go over it.
Continuity mistake: In the night surfing scene, as Johnny gets up for the first wave, he is riding regular (left foot forward), but as the camera cuts back and forth he jumps back and forth between this stance and goofy (right foot forward). All other surfing shots of Johnny in the movie show him surfing goofy.
Continuity mistake: In the stakeout at Latigo Beach, Pappas is surveying Utah's surfing activities from a parked car with binoculars. Pappas takes off his sunglasses and puts them on the dashboard. Watch the sunglasses change position from upside down to right side up for no reason and in a matter of seconds between shots of Pappas watching Utah surf and then especially when Pappas and Utah are communicating on the radio. (00:32:35)
Other mistake: When the guy shoots himself in the foot, there is a close up of the gun as it fires. If you watch it carefully you can see that when the gun fires it's pointing outwards, not at the guy's foot. More obvious in slow motion but not necessary.
Factual error: There is no way Utah could have gotten information about Tyler's parents' death, let alone the city and year, from the computer he was using at the FBI office. He would have had to run a separate search for that information using other sources. That type of personal information is not contained in any crime information database.