This last update to iOS 9.3.4 took over 2 hours to install! So of course no cgm data during this time. I did it last night 'cos I was a little higher at bedtime than I liked and I figured a low wouldn’t be an issue since the update process might take 20 or 30 minutes tops. Ha! I’ve got the receiver working now (took a hint from another thread and used a cable from an old phone to charge it) so getting an alert wasn’t an issue. But I can’t see why the update took so long. Okay, just had to get that off my chest! 
My phone and iPad took 15 minutes each, tops. Did lose the signal but came back on quickly. Don’t know what causes the long wait.