Device: Deco XE75 (latest firmware)
iPhone 16 Pro (WiFi 6E capable)
Vizio V505-G9 Smart TV (2.4/5GHz only)

Issue: Chromecast and AirPlay casting completely broken when iPhone 16 Pro is connected to the 6GHz band. The Vizio TV could not be discovered by Netflix, YouTube, or AirPlay. MLB TV partially discovered the TV but failed to connect every time.

All devices were confirmed on the same SSID. No separate 6GHz SSID — single unified network name across all three bands. AP Isolation is off. IPv6 is off. Local Network permissions confirmed on iPhone. TV confirmed with a valid 192.168.68.x IP address.

Root cause confirmed: The Deco XE75 is not properly bridging mDNS/multicast traffic between clients on different bands under the same SSID. The iPhone on 6GHz and the Vizio on 5GHz cannot discover each other for casting despite being on the same network name.

Workaround: Disabling the 6GHz band entirely forces the iPhone to 5GHz, and casting works immediately and reliably.

This is a firmware-level mDNS proxy issue between bands. A proper fix would either bridge mDNS traffic across all bands under a unified SSID, or add a configurable mDNS proxy option in the Deco app. This issue will become increasingly common as WiFi 6E devices (like the iPhone 16 series) become the norm while many smart TVs and IoT devices remain on 2.4/5GHz.