You have an intermittent problem.
The unit is messing with you. Same principle as it is broken till a tech shows up, then it runs just fine.
The most likely culprits are the timer or thermostat.
I would replace both as the are not too expensive and it is cheaper than throwing out food.
Defrost timer in the "Controls" section shown as Item 23A at the bottom of the list = $17.89
Defrost thermostat in the "System" section Item 21 = $13.89