Duplicate notifications on iOS after upgrade from legacy app

[gnprice]

We've had a couple of reports of users seeing two notifications for each message:
#mobile > received notification twice @ 💬

All the reports we've heard are on iOS, and this is one area whose implementation is pretty separate between platforms, so it appears to be iOS-specific.

We also heard no reports of any symptom like this during the beta period. So it seems likely that the cause of the issue is related to the upgrade from the legacy React Native app.