Nabu Casa & Local Devices Offline After Upgrading to UniFi Cloud Gateway Fiber

Hi all,

I’m looking for some troubleshooting help after upgrading my network setup.

I recently migrated from a UniFi Cloud Gateway to a UniFi Cloud Gateway Fiber (UCG-Fiber). I performed a full backup of the old gateway and restored it onto the UCG-Fiber.

Setup Details:

• Home Assistant: v2026.8 (Standalone on Raspberry Pi, non-container)
• IP Allocation: Home Assistant is on a static IP, connected via Ethernet directly to one of the UCG-Fiber's LAN ports (same physical setup as before).
• WAN Connection: My fiber line connects directly to the UCG-Fiber now (previously ran through an ISP modem/bridge setup).

The Issue: Since the swap, Home Assistant has lost connectivity to a majority of my local smart devices, and my Nabu Casa (Home Assistant Cloud) connection is completely offline.

Traffic Details:

• Checking the UniFi dashboard shows active both outbound and inbound packet activity on the Raspberry Pi's port.
• Basic layer-2/layer-3 traffic seems to be moving, but higher-level application communication (Nabu Casa HTTPS handshakes, local device API sessions/mDNS) is completely failing.

Has anyone run into DNS, MTU/MSS clamping, or mDNS/VLAN issues after restoring a UniFi backup to the Gateway Fiber with a direct fiber connection? Any pointers on what to check first would be greatly appreciated!