Beats One turns off Airplay?
It seems to be either a bug or a rights issue with Beats One. There is no fix at the moment.

A workaround is to choose your Airplay device as the system output. Option + click the sound icon in the taskbar and choose your Airplay device, or select it in Sound settings.

Source: http://www.mcelhearn.com/you-cant-play-beats-1-radio-over-airplay-from-itunes/