@rob_kouw, you may want to open a bug report at GitHub to ensure that your observations are not lost.
The form there also asks you to provide the missing meta-data: device used (likely an Xperia 10 III), SFOS release used, software version used etc.
Please also denote what “the app starts up with a nice UI but without any content” exactly means: Does it work fundamentally, when you browse for a specific music file, i.e. does it play music? Note, that others had better experiences.
Thanks!