Device suddenly stopped sending data

My device (Adafruit feather M0 with LoRa) successfully started sending data to my gateway (IMST+Pi3). I’ve integrated Chirpstack Server with InfluxDB and Grafna, and I’ve created a simple dashboard.

However there were intermittent gaps, and suddenly it sopped sending data since yesterday (I’m attaching a screenshot of the Grafana dashboard - the breaks can be clearly seen from the trend chart). I verified my gateway, it was down for sometime, but even after ensuring its up and running, its not receiving any packets.

Any insights? Any troubleshooting guide would be of great help.