Likewise with any other UPnP Control Point clients, they won’t work with dCS for gapless playback, you have to use Mosaic Control.
See; Bartok Gapless Playback - is it possible? - #2 by Andrew, specifically;
Please note that no third-party control apps (MConnect, BubbleUPnP, etc) will achieve gapless playback with any of our products. This is due to the fact that the internal playback architecture isn’t actually UPnP so the method that these apps use to accomplish gapless playback doesn’t exist.