One of the processes killed automatically PIDS dlrssmsd =

Dears;
I exactly follow the same steps as mentioned in below link,

everything went fine, able to send message as well but after a day i saw one of the process is automatically killed.
here is details.
[root@localhost ~]# playsmsd check
PLAYSMSD_CONF = /etc/playsmsd.conf
PLAYSMS_PATH = /var/www/html/playsms
PLAYSMS_LIB = /var/lib/playsms
PLAYSMS_BIN = /usr/local/bin
PLAYSMS_LOG = /var/log/playsms
DAEMON_SLEEP = 1
ERROR_REPORTING = E_ALL ^ (E_NOTICE | E_WARNING)
IS_RUNNING =
PIDS schedule = 29668
PIDS ratesmsd = 29670
PIDS dlrssmsd =
PIDS recvsmsd = 29674
PIDS sendsmsd = 29676

playsmsd sendsmsd #hanging not exited

[root@localhost playsmslog]# ps ax | grep sms
20159 ? S 8:08 /usr/bin/php -q /usr/local/bin/playsmsd ./playsmsd.conf schedule
20161 ? S 6:21 /usr/bin/php -q /usr/local/bin/playsmsd ./playsmsd.conf ratesmsd
20163 ? S 8:41 /usr/bin/php -q /usr/local/bin/playsmsd ./playsmsd.conf dlrssmsd
20165 ? S 7:48 /usr/bin/php -q /usr/local/bin/playsmsd ./playsmsd.conf recvsmsd
20167 ? S 6:43 /usr/bin/php -q /usr/local/bin/playsmsd ./playsmsd.conf sendsmsd
29668 ? S 8:01 /usr/bin/php -q /usr/local/bin/playsmsd /etc/playsmsd.conf schedule
29670 ? S 5:58 /usr/bin/php -q /usr/local/bin/playsmsd /etc/playsmsd.conf ratesmsd
29674 ? S 7:41 /usr/bin/php -q /usr/local/bin/playsmsd /etc/playsmsd.conf recvsmsd
29676 ? S 6:34 /usr/bin/php -q /usr/local/bin/playsmsd /etc/playsmsd.conf sendsmsd

Machine: centos:7
MariaDB [(none)]> SELECT VERSION();
±---------------+
| VERSION() |
±---------------+
| 5.5.52-MariaDB |
±---------------+

I did not find any issues in log as well, and i could send sms as well…whats wrong with process?

anyone can look the issue?

I have tested watchdog on crontab in every 5 minutes but still this is not a permanent solution,
someone can suggest on this?