The ‘Now playing’ list is downloaded ‘on demand’, which means that only the tracks shown on the screen will be downloaded. This saves bandwidth and memory on your phone, as well as making the first load a lot quicker. Nevertheless, a long list will take more time to initialize than a short list. That’s just how it is. Everything is optimized, and a list of around 1000 tracks should take at most a few seconds to initialize. After that, tracks will be loaded as you scroll, with a little or no delay.

If you have a lot of album art embedded in the music files, that might slow down the loading. If so, it is recommended to export the art (save it in image files instead), or deactivate album art (checkbox in server settings) if you need very responsive long lists.