I'm in the same situation. iPhone 6s running iOS 10.3.1, Garmin Glo/integrated receiver. Mine doesn't even make it more than a couple of hours. I've experienced similar logout staying on the network, turning airplane mode off/on, wifi on/off, etc. It just doesn't want to play nice. Possibly security settings by my organization put onto my phone, but it makes Collector unusable in its current state. As a backup, ESRI should really try to develop a usb cable option to reconnect through laptop on VPN. This wifi stuff is very very stressful for someone about to go into the field...
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