Hi Vlad,
playing audio files from resources is troublesome with Qt 5 at the moment and we have reported this as a critical bug to Digia which will hopefully be fixed with the next Qt release.
At the moment, you can do the following to work around this bug:
1. Do not use the BackgroundMusic element, but instead the SoundEffectVPlay component and convert your music to a wav file. That way you can keep the qrc deployment.
2. Switch to non-qrc deployment (but with assets folders). See the Squaby demo .pro file where this is done because of the same reasons.
Please watch the changelog of the next Felgo updates to get notified when this bug is fixed by Digia and incorporated to Felgo.
Cheers, Chris