Hello,
I assume, this data extension does not require any configuration from the device side? It is simply enabled by your IPS on your subscription plan?
Have you checked, if any SMS messages are sent to the device providing any additional details? SMS database can be accessed from router's WebUI Services -> Mobile utilities -> Messages page.
Does pressing Restart connection from router's WebUI Status -> Network -> Mobile page reconnect successfully?
If yes, could you try to configure periodic pings to some remote host for connection health checks and automatically restart connection in case of disconnect? To do this, login to router's WebUI, navigate to Services -> Auto reboot -> Ping/Wget reboot. Create a new or edit existing default instance, enable it, set Action if no echo is received to Restart mobile connection, adjust other settings, if needed, otherwise, leave default values.
Otherwise, I would like to see, what happens within the device, when the data is used and then additionally increased. Please replicate this, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue.
Best regards,