The Skype UWP app for Windows 10 (phones, tablets, Desktop) has had a rough and buggy evolution and, even today, isn't trouble-free for everyone. As a result, Microsoft has been hinting at (yet another) new implementation of the comms app, with 'preview' users on Windows 10 Desktop/Hololens/XBox (and Andromeda, in the future) able to play. The new Skype UWP app is built on the framework, i.e. effectively all in Javascript. As a result, it's reported to be even slower to start and more resource-intensive (what a surprise), though it does mean that iOS, Android and Windows applications may someday be using the same codebase.
Meanwhile, all this means that further development of the original Skype UWP, as modelled on Windows 10 Mobile phones, has been frozen, aside from critical bug fixes.