When you use a stream that uses a vsrc value, it will go to one of the sources in [v0, v1, v2, v3]. If you leave one such stream open when rebooting the system, the list of vsrcs drifts to [v1, v2, v3, v4], leaving v0 inaccessible and creating a nonexistent v4

This isn't a bug that breaks anything except for any streams that uses a subprocess to keep an eye on the amplipi-side state such as the upcoming #1063 that adds a listener to Spotify streams to watch the volume(s) of the connected zone(s) to synchronize the volume across both the Spotify client and AmpliPi, I suspect a similar method would be used for airplay as well