What kind of machine do you have.Mine is a Gammill.When loops happen,The check spring is the problem.When the needle goes down into the bobbin case,the thread has slack.The hook on the check spring takes out the slack as the rotary hook picks up the thread.So if the check spring is bad it doesn't take up the slack and you get loops.I don't know about why going backward.But that is my 2 cents worth.