I was on that core team and that's not quite what I recall regarding the core library. We had some hard requirements on that library because of protocols used

I was on that core team and that's not quite what I recall regarding the core library. We had some hard requirements on that library because of protocols used by the backend and other reasons. And when you mention features "mostly related to playback", well, it was 95% of the library from its conception (the rest being login and communication with backend). Most of it is quite complex code and not anything you want to rewrite for each platform (mainly offline storage, remote control, playback). The issues we had were caused by growing pain from having the library initially mixed in the desktop code (back when mobile wasn't a thing). It needed to be extracted, productified and a whole lot of tooling and testing written for it. Once we got there, the quality of the code was much nicer and the integration in the various clients easy and automated (which it couldn't be at first). It certainly took sometime, but it wasn't a problem caused by it being cross platform, only that we needed a better infra. We were there when I left the company about the same time as you for quite a while already. The integration with various clients got later easier once we removed the need to reach into that library for just fetching simple server side data. But that wasn't a cross-platform library issue, it was mainly a backend issue.