Default php.ini and .user.ini should always configure the PHP environment.
Some sessions are created in an alternative/default environment that I don't recognize. These session files always mention AUTHENTICATED_TO_DAV_BACKEND suggesting there is an OC app or other feature not using the correct php.ini file. I'm not sure how to go about debugging this situation.
Operating system: Windows 2012
Web server: IIS
PHP version: 5.6
ownCloud version (see ownCloud admin page): 8.0