I tested all channels from 36 to 140 with the original firmware when I bought the router and they worked fine with my clients but WAN connection issue. The router connected to my ISP with 100Mbps. I have a Gigabit connection. I decided to update the firmware to solve the problem. Asus fixed the bug but the wifi started to struggle with my clients.Not all clients support DFS channels.
Could it be the firmware?
I might buy an Asus usb-ac68 or a Netgear A7000 adapter.