Motion Alert Clips....don't show the motion

This happens occasionally with the Pan Cam I have at our primary location.

In the preview of the clip, I can see what caused the motion; a vehicle or a person in the driveway. However when I play the clip, it doesn’t capture the actual motion. It’s a 12 second clip of no motion! It’s really strange and not sure what causes it. At least I can get a small preview of what the motion was in the clip icon.