Please check usb/ sd card copying.
Sometimes it works perfectly (all kind of files), mostly it takes approximately forever (data files and mp3) and even more often (when copying mp3) the result are corrupted mp3 files. And so far it is not reproducible for me, but rather a gamble and no solution provided on the Internet/community has worked so far.
Since the Ver. 18.04.03 it has become a bit better but still not perfect.
That's all. Otherwise just a perfect OS for me.
Cheers