After young Garp tangles with Bonkers the dog, Jenny complains to Stew Percy that Bonkers bit Garp's earlobe off; and Garp's right ear is bandaged. At no time in the remainder of the film do we see any evidence of Garp's ear having been damaged.
The plane hits the house. A section falls with a window with glass yet there is no sound of glass breaking.
When Garp and his family are playing touch football at Dog's Head Harbor, it is the afternoon, In the next scene, where Garp and Roberta are talking, the sun is shown setting over the ocean. This could not occur as Dog's Head Harbor, New Hampshire is on the east coast of the United States, so the sun should be rising.
As Garp is chasing the errant truck driver for the second time, as they run around the front of the truck the boom mic is seen in the windshield of the truck and it is partly disguised with leaves to look like a branch. It comes down from the upper right of the windshield and wiggles a bit.