Based on comments on a few other threads here, it's clear that I am not alone in having long intermintant dropped data between the Dexcom G5 transmitter and an iPhone running ios 10.x (10.2 in my case.)
I'm not convinced this is a dexcom problem. If you search the apple support forums for bluetooth on ios 10.x, they are filled with complaints about all sorts of devices dropping. My daughter's new iphone 6s goes for extended period of times without receiving data from G5 transmitter even if it is right next to it.
Meanwhile, G5 receiver, much further away, has had no problems with connections. Both devices are connecting via bluetooth, which leads me to believe that some, if not all, of the fault here lies with the apple end of things.
On the other hand, iphone seems to work fairly reliably with bluetooth speaker, but this could be because it is less sensitive to initermittent drops.)
There are a number of "fixes" proposed for this issue, none of which I've had time to try yet. (In increasing order of drasticness, they are : Turn bluetooth on and off. Have iPhone "forget" the G5, then reconnect. Rebuild iphone from scratch.)
If anyone has more information about this problem, from Apple or Dexcom, I'd be very interested in hearing about it. The only reason we went with an apple phone (rather than Android) was because of the availability of the G5 mobile app. I'm starting to regret that decision.