You're going to hate reading this... My sunshade did the same thing for nearly one month. When I finally went to the dealer the SA got in the car, pushed the button, and it "magically" went up. I haven't had an issue since.....
He did say that the track is sensitive and a minor bump can jostle it into just the right position to freeze it and that an equally minor bump can get it unstuck. I think it's similar to a folding ladder. If you push just one leg it'll never close, but apply even pressure to both legs and it folds like it's greased with warm butter.
I would tap it right or left a little and try the button again. If that doesn't work, leave the pulling and prying for the SA. My SA said he was ready to replace the whole thing if it didn't begin working. Oh, and they did lube it after they got it up. Don't know about any DIY solutions though.