Motive streaming to UE5.3 on LAN - not working

[rcssd]

Hi,
We've got Motive 3.0.3 running on one computer, UE 5.3 with the Optitrack LiveLink 5.3 v2 plugin on another, and both are hardwired to the same router, so they're on the same local network. Motive streaming is set up with the Local Interface IP being the one assigned by the router (192.168.1.10), and set to Multicast and all data types turned on. In Unreal we create a new optitrack source in livelink, with the server address set to the same IP (192.168.1.10). The source is created and shows the status Disconnected. Motive is actively playing back recorded mocap. Both machines can ping each other (when I activate the Core Networking ICMP Echo service in the firewall on both machines) -- so they are definitely connecting through the router. We've rebooted both machines, restarted UE and Motive multiple times, tried recreating the livelink optitrack source a hundred times -- nothing seems to work. It is always "disconnected" and not receiving data.
What are we missing?

Thanks.

[restroomoblongata]

What version of Motive and the OptiTrack LiveLink plugin are you using?

tunnel rush