our flight from grand rapids mi to O'hare delayed over 5 hours due to weather in Chicago. Ok understandable, BUT united's gate agent rebooked us on American out of O'Hare which was fine. However she took out GRR boarding passes then sent us to terminal to re ticket our bags & get boarding pass from American for Chicago to Cancun flight. We were unable to get back thru security since she had taken our boarding passes and given us receipts instead. we had to go back & wait in line at United in the terminal to get new boarding passes so we could actually fly to Chicago. This caused us to miss our flight. We did get to Chicago eventually but once we got to Cancun 8 hours late, my suitcase stayed in Chicago which was one of the reasons we went to the terminal to begin with. Very frustrated with gate agents and United in general. don't expect them to do anything but feels good to vent!