septic pump keeps running

Whats going on here ? The septic tank fills up ,the pump turns on but doesn't pump anything. After the tank fills and the alarm goes off I can shut off the breaker to the pump for 1 minute and when I turn it back on the pump works fine and will pump the whole tank and shut itself off when empty. What causing this? Thanks

A pump guy would want to know what brand, type, date of installation, and even a picture/diagram of the system if possible.