Roon uses a technology called multicast for device discovery. Multicast has been around for decades and is a very stable solution for the problem of trying to discover things on a network. In its simplest configuration multicast traffic gets repeated to every device on a network and the devices that aren’t interested just ignore it.
Problems arise when networking gear attempts to be smarter than it is and tries to determine who really needs to receive the traffic. This can work very well for large networks running on real hardware, but all of the switches, routers, and WiFi access points need to be working in concert. In home network gear this is rarely the case.
What’s most likely happening is that your Apple router is seeing a lot of multicast discovery traffic coming from the core that is destined for another WiFi device and it assumes that this can’t be right. In a worst-case situation multicast on WiFi can turn into a packet storm and cripple the network. One of two things was likely happening. Either the Apple router reset its radios in an attempt to prevent a storm or the storm actually happened and that took down the WiFi portion of the network.
I will occasionally see similar behavior on starting Roon on my iPad (everything else is wired) where the access point gets concerned and resets the entire WiFi network. This is extremely infrequent for me and it’s likely due to a bug in my access points. I’ve been too lazy to update their firmware.
I’ve had way too many issues with the Apple AirPorts and Sonos / UPnP that I stopped using them a couple of years ago. Everything has been much better since then.