Loss of control track. You need at least 6 seconds of control track before your selected in point. Start your in point at least 6 seconds beyond interruption. You know your tape has video, yet when you play it back, it is snowy or distorted. Stop machine and find Studio Tech.
Levels are too high or limiters on while adjusting.
Adjust levels with limiters off. Lots of little black dropouts flash through your tape, grainy, noisy video, constant head clogging, short black lines horizontally trailing picture transitions. Get new tape. There is no fix for the bad tape you are using. After editing for some period of time, suddenly none of your functions are responding in the usual manner.