Happened to me a lot. Still don't know how.
Maybe after you get back to cubing, you turn the cube slower and more carefully, which means less number...
you should solve it more. like when your driving on the highway, or riding your bike, or while doing push ups, or while juggling. any way to make it...
If there's a flipped edge, you will need to flip that edge along with the buffer piece at the end. You can use M' U' M' U' M' U2 M U' M U' M U2 or R'...