RE: shot completion?
Probably mental.You are not focused and you drop your arm and basically fall out of the shot.The bad shot gets your attention and you refocus.
This is why a shot sequence is so important.Develop a routine and do it religously EVERYTIME.
Another great reason to use a back tension release.
Are you left handed? Most righties when they fall out of a shot hit low left.
Or it could be target panick.