@ottawa_admin on many linux distros resolv.conf tends to have a blurb similar to this "# This file is managed by man:systemd-resolved(8). Do not edit." I can't remember how the ES works but that's something that will burn you if it's not configured correctly.
Restarting the mango service itself would not affect it since this is a system level function. What you'd need to do is restart the whole ES so that Linux reboots and then have a look to see if your entries are still there.