There is no difference between unbleached and bleached AP flour except bleached flour is whiter and has less vitamin E than unbleached. However, AP flour is a blend of hard and soft (high and low protein) flours - and the ratio changes between mills and areas of the country ... so you could be having problems because of using different brands of AP flour - assuming NOTHING
else in your recipe, ingredients, technique, baking sheets or oven has changed.
You might pay a visit to Baking911.com
- especially the Cookies: What Went Wrong?