to diagnose issues like yours, the fastest check is to try other 'data' sources. Does it work at home? does it work when connected to SSID xfinitywifi ?
many wireless routers in a work environment do not allow various mixed data 'port' usage by default. You might ask around to test the issue if someone has t-mobile and if so, if they would help you test by providing a wifi hotspot for a few minutes to allow you to connect to their cell phone data stream and see if the app works fine then. It is outside of Comcast's control if the data stream is not fully available while on other people's networks.