@Grady_Viramontes, it would be really helpful if you provided additional information. For instance, any messages under Settings > Roon ARC, or seen on the Nexus.
Likewise, if the Roon app on the Nexus can’t find your core, please provide details under Networking Gear & Wi-Fi, including all network equipment, and how the core is connected.
If your core is connected to the ISP router, and mobile devices are connected to the mesh, each might use a different subnet.