SIM900 MQTT subscriber skipping data

What all are the constraints of using SIM900 GSM/GPRS modem in a real time data collection project?
Trying to receive multiple bytes of data every second from the CLoud MQTT broker, but sometimes it skips data of 1 second.

Its a 2G module and you can expect some breaks in connection or data loss. Getting 1 second update on a 2G module is quite good.