I have been using the router for almost 3 months now and noticed one particular/hardware issue with Archer A9. Had a chat with customer support as well. 
 

Problem: The wifi disappears randomly. No device in my house is able to search wifi but in the router the led lamp shows both the 5ghz and 2.4ghz wifi are up. 
 

Turning wifi on/ off from the app doesnt help. 
only way to get wifi working agian is to restart the router. I have noticed this issue once in week or two when 15 or more devices are connected to the router.

The issue seems less pronounced when fewer devices are connected.

Other major issues with Archer A9:

1) 2.4ghz band is unstable on older devices. Auto bandwidth selection is disabled and 20Mhz bandwidth selected for 2.4ghz wifi. Still sometimes the old devices get disconnected.

Dissapointed by the performance of 2.4ghz band

2) Turning on qos and firewall refuces the speed.

Yesterday i downgarded the firmware to pervious version and it seems the range and speed has increase. Yet to encounter any issue with wifi.