Hello,
Could you reattach the troubleshoot?
Have you tried to downgrade to the previous firmware and check if the device works properly?
Also, could you connect to the router via SSH (for example PuTTy client) or CLI (in the WebUI navigate to System -> CLI), use root as a username, your web interface password and post a screenshot of the following command:
There might be a modem hardware issue.
Best regards,
Žygimantas