Sophos XG230 + Sophos APX320 + Google Nest Hub: Issues connecting Google Home App to Google Nest

Hi All,

Current Setup:
I have a Sophos XG230 Firewall, and several Sophos APX 320 Access Points.
On these access points I have configured multiple VLANs. One of the VLANs is used for mobile devices. I have configured a Wifi network to connect to this VLAN as wel. 
DHCP Server is the Sophos Firewall.

I have configured an ACL to allow any traffic outside, to WAN. Client Isolation is disabled on the Wifi network. Multicast forwarding is enabled.

I have 2 Google Chromecast devices connected to this wifi, and Laptops connected to the mobile device network can use the Chromecast fine.
However, recently I connected a Google Nest Hub(V1) to this network. The Nest Hub is connected, and has a IP address.

When I use the Google Home App on my mobile device to connect to the Nest Hub, an error is displayed: device not available. Check if the device is connected to the same wifi network.

What am I missing?