I try to minimize my online footprint and don't use iCloud. My iPhone SE runs iOS 13.3 and has an Exchange account which I synchronize at home (over WiFi) with my laptop's Outlook . I only sync Contacts, appointments, and notes .
This morning, I made a call from my work site, so I know my contacts were OK. I then shut the phone off as phones are not permitted at my desk area. At noon, I turned on the phone and all information associated with my Exchange account was gone. Other things (e.g., photos, text messages) were still present.
What could possibly explain this, and how can I prevent it in the future?
I highly doubt that an update occurred between the time I made my last call and the time I turned the phone off. Turning the phone off and on does not cause the Exchange account's information to come back.
Afternote: I recovered in the evening at home. I deleted the Exchange account to which the lost information belonged, recreated it, and resynched with Exchange. However, my question still stands. Thanks.
 While not necessarily relevant to the problem, I use AkrutoSync to interface with Outlook and present an Exchange interface to the iPhone.
 For email, I use Navigator to access a webmail interface.