Comment 7 for bug 1878005

The "protocol" exit is seen a few times in regard to stricter PID handling, for example:
- https://unix.stackexchange.com/questions/493187/systemd-under-ubuntu-18-04-1-fails-with-failed-to-create-user-slice-serv
- https://github.com/systemd/systemd/issues/8085

Chrony sets:
PIDFile=/run/chronyd.pid

And on a normal system that is fine - the pidfile content matches the daemon.

But in your log this detection seems to go wrong as seen on "New main PID 1224 does not exist or is a zombie."

The start wrapper itself worked fine it seems:
ExecStart=/usr/lib/systemd/scripts/chronyd-starter.sh $DAEMON_OPTS (code=exited, status=0/SUCCESS)
So it seems to have died later.

@Jason - in the error case could you on top of
  $ systemctl status chrony
also run the following:
 $ cat /run/chronyd.pid
 $ ps axlf | grep $(cat /run/chronyd.pid)
 $ ps axlf | grep chrony

And attach that output as well - just so we can see if there is a pid left running that hangs and/or if it is fully dead.

Also we might want to check directly if and why the service dies.
So if above no process is running, pelase do as root:
  $ source /etc/default/chrony
  $ /usr/lib/systemd/scripts/chronyd-starter.sh $DAEMON_OPTS
  $ echo $?
  $ ps axlf | grep chrony

And report that as well.