It is likely to be an issue with the router's firmware. We found that UPnP implementations often have bugs, the most common ones being:
- Some routers stop increasing their upload/download counters after reaching the 4 GiB mark (2^32 bytes).
- Some routers freeze or crash when UPnP is polled every second (which is what NetWorx does).
Unfortunately it is not clear which one is your case.
If your router supports SNMP, you can try using it instead. SNMP is normally a better option and usually works well. If your router doesn't support SNMP, I am afraid there is nothing we can do.
You can also try this third-party application,
UPnP Gateway Traffic Monitor, but it will probably produce the same results.