When Michael has his plastic surgery consultation, his face gets marked up in ink for the surgery. When he has left the room to go mingle with the other patients while awaiting surgery, the markings on his face have all disappeared.
As K.I.T.T. first approaches the car-transporter, a pair of hinged swing-down loading ramps are clearly visible on the back of the truck's platform, stowed in the "up" position. But later, when K.I.T.T. backs off the auto-hauler again ("Thanks for the lift!"), he just rolls off a seemingly solid sloped platform; there are no ramps on the truck. And then when K.I.T.T. has landed back on the road and prepares to turn around and drive back to where the bad guy's pickup has stopped, the ramps are visible again, still in the "up" position.
In one scene, where K.I.T.T. is getting ready to drive through a wall with two monks inside, in one shot from above, the monks are briefly not in the car.
The small bag that the thieves carry the jewelry in during the robbery at the beginning clearly has some red markings and stripes on it. After the robbery when they stop to split it up, the bag is plain black all over.
When Michael is first questioning Jody about the robbery, she starts telling him and her failed attempts at skiing and scuba diving - the back of Michael's shirt is visible and it's completely dry. Moments later, when Charley enters and Devon calls, the back of his shirt is visible again and it's suddenly covered in sweat.
Franciscan Friars are not known for running entrepreneurial enterprises such as wineries. They are mendicants and known for being supported through charity. It would have made more factual sense to have the winery run by Cistercian Monks. In fact quite a few wineries are run by Cistercian Monks, even in California. Moreso, Franciscans are not called Monks, but Friars.
When Michael stops at the entrance of the small pipe where the two thieves escape, KITT clearly has a standard circular steering wheel, rather than his customized steering wheel.
When K.I.T.T. drives to meet Michael pulling his prisoner out of the river, the stunt driver behind the driver's seat is extremely obvious as K.I.T.T.'s windows are down and the roof is off, giving very clear and unobstructed views inside the car.
When Michael pulls Charley from the river, he slams him on KITT's hood and the dashboard is clearly visible - it's the Season 1 & 2 dash, rather than the current Season 3 dash.
When Michael is injected with the sedative, the actor clearly isn't David Hasselhoff - the hairline and overall build are both completely different.
When KITT Turbo Boosts onto the car carrier, his wheels are clearly chained onto it in the next scene.
After Michael jumps into the river, he stands up and reveals that the river is so shallow that he should have sustained severe injury from the jump. Stuntmen probably jumped into a deep section of the river, but then they had David Hasselhoff stand up in much shallower section after the cut.
In the K.I.T.T./vehicle-carrier/pickup truck chase scene, one of the camera crew members evidently gets his hat blown off from the breeze created by the moving camera truck - you can clearly see a dark-colored baseball cap fly off from behind the camera's view and go tumbling down the highway on the right side of the frame.
When KITT is backing up to help the monk with the overturned cart, two light stands and a Fresnel lens spotlight are visible reflected on the driver side door.
Michael uses the grappling hook to assist Brother Francis - after he gets into KITT and starts reversing, the entire camera crew is reflected in the door.
When Michael pours the diamonds from the crystal vase into the handkerchief, he doesn't get them all - a good half-dozen or more are left sticking to the inside of the wet glass. According to the story, the diamonds were extremely valuable, so Michael would surely have made absolutely sure to retrieve all of them, even if it had meant taking a few more precious seconds to do so.