Found this https://steamcommunity.com/app/108600/discussions/6/152392786914782918/ after having this issue myself several times. It seems to happen when you don't have a constant supply of electricity, i.e. you turn off the generator for short periods to refuel. At a later time when you remove food to make meals or move things around it will unfreeze and instantly rot. I posted a little more detail in the above thread.