I have also seen this in an app where I use playlist.
I think it’s a bug, you are using it as advertized AFAICS.
Maybe some gdb
or strace
magic can reveal where it fails.
Qt source is here but I can’t really read that.
I have found this which sais:
So maybe it’s that the app can’t access the PersistentStorage path or database for some reason? If so there’s some discussion about that here.