I run a handful of FreePBX systems and all are based on the distro. I have noticed that on several occasions when making changes in the Sysadmin module (on at least 2 or 3 of them) and possibly only in the “Notifications Settings” section that upon submitting changes the webserver will die as will any calling. I normally have to do a full system reboot to get everything back. I am digging through the log files now looking for something to post.
If you track it down, please make sure to open a bug ticket at issues.freepbx.org so it can get eyes on it from the development team.
I just recreated and crashed a system I will log it at the issues site now.