I am in the UK (v2 Hub) and about 10 minutes ago my hub has sent over 30 notifications in the space of a few minutes.
Opening closing contact sensors, motion sensor firing off.
No doors were opened (I have a camera on the front-door) and the motion is near there too.
This has never happened before - I have been pretty lucky with reliability of my hub.
Recently I started seeing notifications for one event repeated multiple times. For instance, a door opening triggers (on average) 3 notification messages. Worst was last evening starting at 16:37 EST when ALL my devices that triggered 3 notifications for one event. This morning all was back to normal.