Missing push notifications

There are several reports of people complaining Riot sometimes misses to notify them like in the [Riot iOS](https://matrix.to/#/!tDRGDwZwQnlkowsjsm:matrix.org/$1513615016584RFucI:madduck.net) room.

I reproduced a possible similar bug at https://github.com/matrix-org/riot-ios-rageshakes/issues/748 where the notification happened with a 3 min delay.
Looking at system logs, they show that the app tried to start at the time of the notification but it fired a 30s watchdog because it was infinitely looping at https://github.com/vector-im/riot-ios/blob/898353e47d0b70486885e322a2bd3620176e2383/Riot/AppDelegate.m#L315-L320

Note: this piece of code was for fixing spontaneous logout (https://github.com/vector-im/riot-ios/pull/1653)

Start with the system-log evidence and the reproduction linked in riot-ios-rageshakes issue 748, then inspect the loop in Riot/AppDelegate.m around lines 315-320. Confirm how the spontaneous-logout fix relates to notification startup, and consider the issue done when notifications no longer trigger the watchdog or arrive several minutes late.

Written by the indexing model from the issue text.