⚠️ Critical Issue: Deco M9 Plus (V2) Guest Wi-Fi DHCP Failure with Wired Backhaul (Firmware 1.9.1)

Since upgrading my TP-Link Deco M9 Plus (V2) mesh system, the Guest Wi-Fi network is failing to assign DHCP addresses (IP addresses) to connecting devices when the units are configured for Wired Ethernet Backhaul. This represents a severe regression from the previous working firmware version.

Specifics of the Problem

Confirmation of Regression

The issue is definitively linked to the new firmware and the Wired Ethernet Backhaul configuration:

1. The network was operating without issue on Firmware 1.8.5 with the exact same wired setup.

2. Switching the system to Wi-Fi Backhaul immediately resolves the Guest Wi-Fi DHCP failure, confirming that the network hardware and core DHCP server are functional.

3. The problem recurs immediately upon switching back to Wired Ethernet Backhaul.

This strongly suggests a bug introduced in Firmware 1.9.1 affecting the way the Guest Network's isolation or routing function interacts with the Wired Backhaul.

Action Requested: Please investigate this regression in firmware 1.9.1 Build 20250612 Rel 45690 and provide a fix or a known workaround for the Deco M9 Plus V2 model.