If the missing shots are truly absent from the negatives, the most likely cause is the camera, not the lab. Missing frames from the middle of a roll point to a film advance or shutter problem, or possibly user winding that didn’t fully advance the film during those shots. Severe underexposure is another possibility, but a mechanical issue is more likely.

A good way to check whether the lab is at fault is to inspect the film itself: if the film has edge markings/edge print running through the blank section, that means that section was developed normally. In that case, the lab did process the film, and those frames simply were not exposed by the camera.

Labs can make mistakes, but blank frames in the middle of a developed roll are more consistent with the camera failing to expose those frames than with processing loss.

Also, on many film cameras, the frame counter is only an estimate. You normally keep shooting until the film won’t advance further, and it’s common to get a few extra frames beyond the number on the box.