Sounds like the device might be bricked. Did you try a recovery / bootloader mode re-flash? See here. I've had to do this a few times.
Thank you for contacting us.
It would be great if you could replicate the issue, then access the router's WebUI, go to SYSTEM > ADMINISTRATION > TROUBLESHOOT section, download troubleshoot file from there and send it to me.
Logs in this file will help to answer what causes this issue.
Thank you in advance.