Hi, I’m not sure if someone else has already addressed this issue for you, but I had the same problem with my ASUS AiMesh setup—my iPhone Roon app was unable to locate Roon Core, unless my phone was connected to the same node on which the Core was running. And if I did successfully connect to Roon and traveled to a different node in my home, the Core would disconnect until I traveled back.
This issue has been raised quite a few times in various threads. The router tweak that resolved the issue for me was to enable multicast routing in the LAN—> IPTV settings in the ASUS GUI. I left all other settings unchanged, and the problem has never recurred. Multicast is disabled by default; it’s typically employed to enable direct connection of cable TV whole-home streaming access points to the ASUS router, when it’s configured via IP Passthrough in front of an ISP’s provided residential gateway.
However, Roon apparently also requires multicast capability to maintain its data connection across all audio devices on the network—by definition the Core functions as a multi-room, multi-device network aggregator, constantly processing two-way traffic to a multitude of LAN clients simultaneously in real-time. That’s basically the definition of multicast routing itself.
The only down-side I’ve found after enabling multicast is that when I subsequently ran the integrated WAN-side internet speed test in the ASUS GUI, my usual gigabit download speeds dropped by about 40%—however I suspect that this phenomenon is an artifact, because speed tests on my client devices remained unchanged and robust.
Hope that helps!