At the end when Von Zipper says "I will return!" to the beach gang, it's still daylight. But seconds before, the gang is gathered around a campfire and it's pitch dark.
When Dolores gets back to Sutwell after leaving him with the razor to shave his beard, his hair is combed straight back and is mostly dark; black in the back and dark brown in the front. From the next scene on, his hair is lighter, brown with some gray lightening, and is combed with a part on the far left.
In the first scene at Big Daddy's - Dick Dale is seen with a large hoop ear ring as he plays the bongo drums and when he initially goes into the loft to play "Swingin' and a-Surfin" with the Del Tones. During the song, the camera goes from the dancing kids back to Dick Dale, but Dale is no longer wearing the ear ring.
When Sutwell succeeds in surfing, the long shots show him with his cap still on. In close-ups he is bareheaded.
The first time Frankie goes surfing, he's on a turquoise surfboard, not one of the surfboards that was in his car at the beginning of the movie.
Early in the film, when Frankie and Dolores drive onto the beach towards their beach house for the first time, there's already a set of tire tracks in the sand from a previous take.
Early in the film, when Frankie and Dolores are driving down the paved highway, a shot from a distance shows a somewhat narrow (two-lane) road with the opposite lane a dark asphalt. Seconds later, a more close-up cab scene shows a much wider highway with no dark asphalt on the opposite side.
After Dolores walks away with Sutwell's glasses, when she comes back and sees Sutwell shaved, he never asks for his glasses back. His vision seems to be perfect from thereon after shaving, as there's no mention of him needing his glasses for the rest of the movie. This is explained in his scene with Morey Amsterdam. He says he grew the beard and added fake glasses in an effort to appear older. Both the beard and glasses are an artifice.