So we just swapped our old iPhones for new ones. We were using them as Presence Sensors in SmartThings.
The problem is, that with all of the phones off (old/new), we both still show as “Present”. With the old phones off, and the new phones on – regardless of whether or not the Mobile App is running – we both still show as “Present”.
Is there something I need to do so that ST removes the association with the old phone and binds to the new?
Turning the phone won’t ever make it report as gone. SmartThings uses the last reported location for presence. You actually have to leave
So the phone can report a location other than your house for SmartThings to show you as gone.
Okay, tried that … didn’t work. 
also, my Sonos has stopped working as well. I’m going to delete and re-add them now and see if that resolves it.
Door contacts and temperature sensors appear to be working still though.
I just tested with my iPhone 6 and it worked without doing anything special. It triggered both ways just across the geofence line.
Sonos on the other hand hasn’t worked for me on SmartThings for a couple of weeks. It stopped when I did the Sonos 5.1 firmware update.
I have an iPhone 6 and iOS 8. No problem here. I just got back from a two hour walk that took me in and out of my geo-fenced area 6 times. Each one showed up as a push notification. (I installed iOS 8 on my iPhone 5 for the 2 days I used it before I got the iPhone 6 and everything worked fine with that configuration.)
I logged out and deleted the mobile app. I re-installed, logged back in, and it appears to be working again. pfew! 