I'm having the same issue with a few of my PWAs. They work fine in Safari, but when installed as a homescreen app, audio playback won't start. It does work once if I restart the phone, but then stops working again if I close and reopen the app. Additionally, it seems that sequential playback doesn't work when the phone is locked. Instead of playing the next audio track, playback will stop until the app is re-focused, at which point playback will begin again.