We actually experienced something similar, over this past weekend, but our [data dump] didn't occur during an iTunes sync, but just the average everyday syncing function. The only issue was that the Collector app decided to install the newest version; 10.3.4, during the sync?
Both of the field biologist reported that during the syncing operation the app simply shutdown, then restarted itself, and all of the data had been lost. When I asked them to send me a screen shot of the App Store for updates, you can see where the app had updated.
Any chance to keep this from happening on future releases or Maybe an announcement email to all AGOL users that the Collector app is going to be updated on such and such date, so we can plan around that release date?