Every new ASUS firmware upgrade is an adventure. I am running a somewhat standard setup. 3 nodes (mesh), all RT-AC68U - one node hard wired and one node wireless. After the latest firmware update (3.0.0.4.384_45717) I noticed my ATT Wifi Calling wasn't working anymore. After a little experimentation, I found that if I disable IPv6 on the ASUS router, I get my WiFi calling back. I've seen similar WiFI calling issues before (ASUS seems to be very good and re-introducing previously fixed bugs),...
ipv6 and ATT WiFi Calling not working
ipv6 and ATT WiFi Calling not working