it is not related to the Active: active (exited). This time the status was Active: active (running) and my inputs were disappearing. The sudo service mqtt_input restart
allowed my input to work as it should.
pi@emonpi(rw):~$ sudo service mqtt_input status
● mqtt_input.service - LSB: Starts phpmqtt_input agent daemon at boot time
Loaded: loaded (/etc/init.d/mqtt_input)
Active: active (running) since Mon 2016-12-19 20:06:57 CST; 17h ago
Process: 32484 ExecStop=/etc/init.d/mqtt_input stop (code=exited, status=0/SUCCESS)
Process: 32490 ExecStart=/etc/init.d/mqtt_input start (code=exited, status=0/SUCCESS)
CGroup: /system.slice/mqtt_input.service
└─32494 /usr/bin/php /var/www/emoncms/scripts/phpmqtt_input.php
Dec 19 20:06:57 emonpi mqtt_input[32490]: Starting Daemon for the emoncms MQTT script: mqtt_input.
Dec 19 20:06:57 emonpi systemd[1]: Started LSB: Starts phpmqtt_input agent daemon at boot time.
pi@emonpi(rw):~$ sudo service mqtt_input restart