Hello, You could have a thermostat problem or stuck in a defrost mode. Or problem in the control circuit of unit. I.E. if has a computer board. Everything today has them. I work on mostly on larger comercial walk-in boxes. Did you put new product in there? Because food has heat content so new items put in will take longer to freeze. Is it over packed so there is no air circulation in the box? Also check your door gaskets if they are sealing correctly. I'm sorry I read your post again I think your unit is not coming out of defrost or intermitently working . Most likely a bad control board. do the warranty route that's what you pay for. Hope something I wrote can help.
Good Luck, John
Good Luck, John