I haven't read the full thread so sorry if this is a duplicate answer:
I once had a problem pulling up the boarding pass on my phone at the gate. The GA suggested that next time I make sure I follow all the steps all the way through and then take a screen shot of the boarding pass. That way it is on your phone no matter what. I can't remember if she then helped me get a paper pass or if the link finally worked, but I didn't miss the flight.