At that situation, you should call support.

Not syncs have no concern with PVCs. If it can not syncs any more, you should check all the physics devices. The router, The telephone line,The Wall socket, The DSL type and Annex type.

Hi Friend. Your issue seems a little complex. I am not familiar with WDS so i think i can not help you. I think you should contact the TPLink support. Well, if you just want to extend your WiFi, why...

Well. if you can not open this post. How about trying to disable Bit swap?

Archer C9 is a wireless router, i think it can not speed up your ADSL internet.

I think you need a VLAN ID