Spotify discovery relies heavily on local network discovery mechanisms such as mDNS / multicast.
Some routers handle these protocols poorly, especially when features like IGMP snooping, Wi-Fi isolation, VLANs, or “smart” firewalling are enabled by default.
In practice, this can result in Spotify Connect devices appearing and disappearing randomly, or not being discovered at all.
This is not specific to Spotycast — it’s a common issue with many network audio systems that depend on multicast discovery.