Have you updated with Keep settings option enabled? If yes, could you try to reset the device to factory defaults over WebUI, as instructed here?
Do you have any remote access options (SSH, HTTP(S)) enabled?
Can you confirm that data is consumed by package_manager?
Could you check if you see any high traffic connections in Status -> Realtime data -> Connections section in the WebUI?
Could you install TCPdump in the router via SSH using commands:
- opkg update
- opkg install tcpdump
And capture some packets to a pcap file with a following command to /tmp directory:
- tcpdump -i wwan0 -n -w /tmp/capture.pcap
I would then like you to extract this file using WinSCP and, by editing your question, attach the packet capture together with a troubleshoot file from the device experiencing the issue. To generate a troubleshoot file, access router's WebUI, go to System -> Administration -> Troubleshoot section and download it from there.