When I kettle my bagels they collapse and look like round white prunes. They taste fine and the texture is good, but they look awful. I "half-proof" them for 15-20 minutes and kettle them for a little less than a minute per side. The dough is stiffer than bread dough and shows a good "window" when stretched. I suspect that either the dough is too slack or there's too much/too little yeast.