NAT traffic is processed by CPU" when WAN Mac is cloned, "PPA (Protocol Processing Accelerator) is enabled" with cloning disabled. Advanced Settings/LAN/Switch Control/NAT Acceleration. This bug was revealed into this thread https://www.snbforums.com/threads/asus-blue-cave-ac2600-dual-band-wireless-router-reviewed.45982/page-4, but it still exists. I hope you will fix it :)