Spotify on iOS supports .mp3 and .m4a, two file formats I use mainly for my local files. However, if I sync an album in the .m4a format to my Spotify app on my iPhone, the album cover doesn't load and instead shows a stock note cover art. .mp3 works fine and loads the art as intended. So the problem resides in the .m4a format as it seems to be not entirely supported, even though Spotify on Desktop and Mobile plays these files just fine. It should be noted that Spotify on a Desktop (PC, Mac) loads the album art of .m4a files without any problems. Although this seems to be shaky at times, as some files just refuse to show album cover no matter what I do (Re-sync, remove the file and then add it again, etc.).
I'm using iPhone 7+ and the latest Spotify versions to-date (18.104.22.1689). Will there be any fixes for this issue?