Look for an email containing something to this effect:
Missing Info.plist key - This app attempts to access privacy-sensitive data without a usage description. The app's Info.plist must contain an NSAppleMusicUsageDescription key with a string value explaining to the user how the app uses this data.
Where the missing key could be any of a range of permissions, and may be something you're not even using. This comes up often for react-native applications especially.
If you get such an email, follow the advice regarding the Info.plist key and then resubmit the app.