Dual-stack routers run IPv4 and IPv6 together. Matter may loop — QR works, Wi-Fi joins, setup restarts — when controllers flip address families or mDNS records conflict.
Signs of a dual-stack loop
Same QR scanned three times without finishing. Device joins Wi-Fi per router DHCP but hub never shows operational. Loop started after enabling IPv6 on ISP gateway.
Fixes
Enable stable IPv6 on LAN per ISP docs; reboot router and hub. Keep phone on same SSID entire session — no switching to cellular. Disable DNS rebinding filters blocking .local during setup. Flatten VLANs for commissioning. Update router firmware; several brands fixed Matter loops in patches.
If loop persists, commission with IPv6 temporarily off on LAN only as a diagnostic — re-enable after success if your ISP allows.
Verify
One commission completes under ten minutes without re-scanning QR.