Continuity mistake: When Jennifer is attacked by the vines, she's holding a basket with her poodle in it with one hand and seconds later grabs the vine with both hands without letting go of the basket.
Plot hole: When the group arrive on the plateau, they are "visited" by a dinosaur. Challenger states it is a brontosaurus. However, no one in the group ever actually saw the dinosaur. No one came in contact with the dinosaur at all except for the roaring sound (this is verified later in the movie). Summerlee doesn't even believe they were visited by a dinosaur at all! How could Professor Challenger even remotely theorize it was a brontosaurus? Plus, later we see it ourselves, and even I could say it wasn't a brontosaurus (it's low to the ground and is eating another dinosaur).
Continuity mistake: When the group finds the dinosaur tracks, Frosty the poodle runs away and finds said dinosaur, but the size of the tracks the men find and the size of the dinosaur don't match.
Continuity mistake: When Roxton finds the diary in the cave, the native girl is sitting down with her left hand on her right leg in long shots and her right hand on her left leg in closeup shots.
Revealing mistake: When Gomez falls into the boiling water/lava mixture, he is obviously a dummy model.
Other mistake: When the character plays the guitar throughout the movie, there are obviously no strings attached to the guitar.
