The script /lib/udev/write_root_link_rule which creates the dynamic rule for /dev/root symlink always creates the rule in /dev/.udev/rules.d even if udev uses /run/udev. Consequently, the rules file is not found and /dev/root symlink is not created. Reproducible: Always
Same problem here, udev-171 no longer use /dev/.udev when /run/udev exists, so /dev/root is not being created and many programs fail to find root device.
This has been fixed in udev-171-r3. Thanks for the report.