Monthly disassociations

[chris_lutka_gam]

This is my first post. Please be gentle since I may not have all the terminology correct.
I have a deployment of 16 r310 APs in my environment, all using a local Unleashed management system. I set my primary network to use WPA2, open authentication, and use D-PSK (mobile friendly) for the key. There is no expiry but D-PSK is limited to 1 device.
The issue I'm encountering is that one user, about monthly, gets disconnected from his Apple iPhone to my WiFi network.
Going through the logs, I see the following entries for his device's MAC address:

Aug 28 14:26:10 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=33,ack_rssi=0,reason=1,freq=5560,chan=112,rx pkt,byte;tx pkt,byte=(6,990,6,654)
Aug 28 14:26:05 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=32,ack_rssi=0,reason=1,freq=5560,chan=112,rx pkt,byte;tx pkt,byte=(6,990,6,654)
Aug 28 14:25:54 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=29,ack_rssi=0,reason=1,freq=5560,chan=112,rx pkt,byte;tx pkt,byte=(5,825,6,654)
Aug 28 10:41:38 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=24,ack_rssi=0,reason=1,freq=2412,chan=1,rx pkt,byte;tx pkt,byte=(5,655,6,654)
Aug 28 10:41:33 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=25,ack_rssi=0,reason=1,freq=2412,chan=1,rx pkt,byte;tx pkt,byte=(5,655,6,654)
Aug 28 10:41:27 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=23,ack_rssi=0,reason=1,freq=2412,chan=1,rx pkt,byte;tx pkt,byte=(5,655,6,654)
Aug 28 10:41:22 HomeImportsWiFi Eved: STA-DISASSOC-REASON [ieee80211_send_mgmt(),4698,send station disassociate] b8:44:d9:xx:e1:25 rx_rssi=22,ack_rssi=0,reason=1,freq=2412,chan=1,rx pkt,byte;tx pkt,byte=(5,655,6,654)

Performing my due diligence, I did search and see many messages but they all seemed to be related to reason=8 yet mine above is reason=1. 
I put the key back in to the iPhone and everything worked as expected. My questions are:
1. What does reason=1 really mean?
2. Would it be the iPhone or the r310/Unleashed system arbitrarily disassociating the device?
3. How can I prevent this from occurring next month?
4. Should I simply regenerate a new D-PSK for the device and wait it out? (I would do this but it doesn't answer the why.)
No other iPhone in my environment is having this issue of course.

[chris_lutka_gam]

How do I mark a question as answered?