Thanks for the replies so far. I've disabled the Bonjour forwarding, but that didn't make a difference, Chromecast works over wireless, and doesn't over a wired connection. I've noticed some oddities:
- Chromecast over wireless shows "Source IP and/or VLAN mismatch" issues in the event log (security appliance), and shows: source_client_ip: 192.168.128.12, source_client_mac: [xx], source_client_assigned_vlan: 1
- Whereas, Chromecast over wired shows it either on VLAN 0 or untagged
- Other devices seem to be on VLAN 1
I didn't change any of the VLAN settings, but perhaps this gives a little more color on what's going on.
P.S. on the multi-cast to uni-cast conversion, I've left that disabled, it really impacted the Google Home and Audio streaming: out of sync audio, and unable to set volume levels across devices in the Google Home app.