Sometimes playback is interrupted when a smartphone notification (text, email) is received or system sound is played (lock sound, camera shutter etc.). Additionally - streaming is not automatically resumed.
The simplest way to avoid notifications/system sound interrupting your music playback is to activate silent mode on all Bluetooth connected devices. Music playback is still working but all notifications/system sounds are muted.
Alternatively, the Bluetooth connection to the speaker can also be disconnected or Bluetooth turned off on your phone.