Gapless playback with 3rd party control apps will not happen. This feature is in place for convenience but as I’ve mentioned before the methods that we use to manage the play queue are not in any way based on UPnP. I’m not going to go into details here as they aren’t very interesting, but suffice it to say that we would need to rearchitect our entire product in order to support gapless UPnP. Given that gapless UPnP playback is fundamentally flawed that’s not even worth entertaining. Yes, BubbleUP does work, but its one of the only ones that does. Over 70% of our customers use iOS and there is no viable UPnP control point on that platform since a proper UPnP control point breaks all of Apple’s power management rules.
We support servers that follow the UPnP standards to the letter. We strongly recommend MinimServer as it is the only one that we have found that does. Lots of others get close and work in many situations, but they all have quirks which cause them to behave in an unexpected way when issued a standard UPnP command.