Because the chipset is different on W9980 and 8960N. So some functions may different. After you set bandwidth rules,you can reboot the router to make it take effect.

Are you log in DDNS on D5 router? What's the WAN IP address of D5 router? You can try to access the router by WAN IP:3000 and check if it will work. If this works,it should be a DDNS problem. Maybe...

Are you log in DDNS on D5 router? What's the WAN IP address of D5 router? You can try to access the router by WAN IP:3000 and check if it will work. If this works,it should be a DDNS problem. Maybe...

The latest firmware for Archer D9 is 160115. You can try to upgrade it and check if it fixed the problem. http://www.tp-link.com/en/download/Archer-D9.html#Firmware

OK,that's good!

What's the format of your USB drive? You can upgrade the latest firmware and check if the USB3.0 works fine. http://www.tp-link.com/en/download/Archer-D9.html#Firmware