During the drugstore sequence following the Royal Garden sequence, the "DrugstOre" sign reverses, facing outside for shots from the outside of the drugstore, and inside for shots from the inside of the drugstore.
In the Royal Garden, a pillar inside the entrance has alternate metal and stone faces which swap a few times, so the side facing the entrance is sometimes metal and sometimes stone.
When the glass door of the nightclub shatters, it's supposed to be because Mr Hulot and the doorman are pulling on opposite ends of the doorknob, the doorman trying to open the door to convince Hulot to come inside. From the outside you can see the doorknob attached to the glass door. From the inside, what's actually happening, though, is the glass door, which has no doorknob, is slightly ajar, with the doorman's foot keeping it open enough for him to reach outside to grab a loose doorknob, which Hulot is also holding. You can see that as they both hold it, it moves up and down, which would be impossible if it was attached to the door. Also, when the glass shatters it's between the knob and the camera.
When the ladies first get on the tour bus at the airport, the license plate on the front of the bus says 1154 RX75. A few seconds later, when the bus is on the highway, the plate says 7604 TM75. When the bus stops and some of the ladies get off, the plate says 1154 TJ75. When those ladies walk around to the back of the bus, the rear plate says 1175 RX75. After the scenes with Mr Hulot trying to meet the man in the glass building, the ladies finally disembark from the bus with the license plate back to the original 1154 RX75.
At the beginning, when the old man is being photographed as he walks through the airport and drives off in the car, one of the photographers' camera flash does not go off despite the photographer appearing to replace the flash bulbs. Instead, separate units set up off screen do, the last one at the car partially illuminating the photographer's back. Also, the other photographer without a flash on his camera never appears to change the focus on his lens the entire time.
The escalator handrails aren't moving in the airport scene. The actors skim their hands along pretending it's moving, when you can see by reflections of its surface that it is indeed not.