The SELinux attributes of /run/ondemand-nginx go away across a reboot, and, (OOD 2.0.18, CenTOS 7) cause SEL errors for nginx when it restarts. Adding /etc/tmpfiles.d/ood.conf containing the 4 lines below seems to resolve this problem; perhaps this file could be added to the ondemand-selinux package?
# SELinux dir creates for Open OnDemand
# Type Path Mode UID GID Age Argument
d /run/ondemand-nginx 0755 root root - -
Z /run/ondemand-nginx - - - - -