It's part of the healing process. You go back a step or two and proceed slowly. It's usually because something the day before irritated you, or your ate the wrong thing for that day and now your tool is rebelling. Or maybe you have more mucus in your tool from drainage. Could be so many things.
We can eat the same thing one day and have no issue and the next not be able to handle it. You just have to eat tiny bites, progress slowly, take your time through a meal, etc. It passes and you eventually have fewer of these days.