The same here! I thought initially that the reason was due to my company´s security policy that I have to install in order to access their email server, but looks like it is a random issue/bug that caught some of us...
To make things worse, the first time I was about to travel, going from the office to the airport, but managed to restore my phone from scratch (had to factory reset though because I did not have my Mac with me to restore a backup). It happened again two days ago and I am in another trip, completely lost without my phone in a hotel room!
This is a serious issue and should be fixed as soon as possible...or at least Apple should have a way to restore software via a web browser...I believe most organisations forbid installation of non-standard software in company notebooks, so iTunes is not available everywhere...
Anyway, if anyone finds a way to stop this from happening, please let me know. Thanks
Gerson
iPhone 6s