Hello,
What firmware version is your device running?
Can you ping anything from the router itself? For example, in the WebUI navigate to System -> Administration -> Troubleshoot -> Diagnostics and ping 8.8.8.8.
I would also like you to attach a troubleshoot file to your question. Please, replicate the issue, 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,