I’ve recently discovered something about those gaps and the frame not hitting the framed mark but falling in the middle.
You can move the audio independently from the video anywhere between the frame and it will stick and not snap to the frame marker. This is good especially when you are trying to remove a click or something. However, when you then move the video it will snap to where the audio event is which sometimes happens to be in the middle of one frame.
Roger Bansemer