I have experienced something similar starting Asterisk 126.96.36.199 on CentOS 7
on commodity / whitebox hardware.
The problem was that Asterisk was starting “too quickly” in the systemd startup sequence, before the required services it needs to run were up and ready.
I eventually came up with this systemd script to start it, and this now starts Asterisk on all our our new CentOS 7-using deployments.
Maybe you can try it out…? This starts our Asterisk 1.8 instances without problems on CentOS 7 on boot: