If a server is hard rebooted (due to crash, power loss, etc.) - a stale PID file may be left over and on subsequent restarts - Bacula may appear to start (and then immediately stop). To test - you will need to run Bacula FD in foreground mode:

/opt/bacula/bin/bacula-fd -u root -g bacula -c /opt/bacula/etc/bacula-fd.conf -v -f

If it indeed does have a stale PID - it should show the following:

user@host [path]#/opt/bacula/bin/bacula-fd -u root -g bacula -c /opt/bacula/etc/bacula-fd.conf -v -f
25-May19:57 servername: ERROR TERMINATION at bsys.c:438
bacula-fd is already running. pid=4000
user@host [path]#

but not actually be in the process list (ps aux)

If this is the case - then simply removing the PID file should resolve the issue and allow Bacula FD to restart normally.