This has happened to me 4 times during fast cross-fade from song to song.
I am working on a set list and just checking how songs are connected so I start a song, manually drag the play head towards the end and then I cross-fade to the next and so on.
When this happens the app freezes.
If I swipe up to go to the home screen the minimised version is no a completely black window. I kill the app by swiping it up and open again. 3 of the 4 time it was a black screen and had to kill it a second time to make it work.