Build fails when trying trying to deploy the 'release' flavor. Apparently the ProGuard files are not up to date.
Note: android.support.v4.media.IMediaBrowserServiceCallbacksAdapterApi21: can't find dynamically referenced class android.service.media.IMediaBrowserServiceCallbacks
Note: android.support.v4.media.IMediaBrowserServiceCallbacksAdapterApi21: can't find dynamically referenced class android.content.pm.ParceledListSlice
Note: android.support.v4.media.IMediaBrowserServiceCallbacksAdapterApi21$Stub: can't find dynamically referenced class android.service.media.IMediaBrowserServiceCallbacks$Stub
Note: android.support.v4.media.ParceledListSliceAdapterApi21: can't find dynamically referenced class android.content.pm.ParceledListSlice
Note: android.support.v4.text.ICUCompatApi23: can't find dynamically referenced class libcore.icu.ICU
Note: android.support.v4.text.ICUCompatIcs: can't find dynamically referenced class libcore.icu.ICU
Note: android.support.v7.widget.DrawableUtils: can't find dynamically referenced class android.graphics.Insets
Note: com.facebook.stetho.inspector.runtime.RhinoDetectingRuntimeReplFactory: can't find dynamically referenced class com.facebook.stetho.rhino.JsRuntimeReplFactoryBuilder
Note: com.google.android.gms.internal.zzanx: can't find dynamically referenced class sun.misc.Unsafe
Note: com.google.gson.internal.UnsafeAllocator: can't find dynamically referenced class sun.misc.Unsafe
Note: com.squareup.picasso.Utils: can't find dynamically referenced class com.squareup.okhttp.OkHttpClient
Note: okhttp3.internal.platform.AndroidPlatform: can't find dynamically referenced class com.android.org.conscrypt.SSLParametersImpl
Note: okhttp3.internal.platform.AndroidPlatform: can't find dynamically referenced class org.apache.harmony.xnet.provider.jsse.SSLParametersImpl
Note: okhttp3.internal.platform.Platform: can't find dynamically referenced class sun.security.ssl.SSLContextImpl
Note: retrofit2.Platform: can't find dynamically referenced class java.util.Optional
Note: retrofit2.Platform: can't find dynamically referenced class org.robovm.apple.foundation.NSObject
Note: retrofit2.Platform$IOS$MainThreadExecutor: can't find dynamically referenced class org.robovm.apple.foundation.NSOperationQueue
Note: android.support.v4.app.NotificationCompatJellybean accesses a declared field 'icon' dynamically
Maybe this is program field 'android.support.design.R$attr { int icon; }'
Maybe this is program field 'android.support.design.R$id { int icon; }'
Maybe this is program field 'android.support.v4.app.NotificationCompat$Action { int icon; }'
Maybe this is program field 'android.support.v7.appcompat.R$attr { int icon; }'
Maybe this is program field 'android.support.v7.appcompat.R$id { int icon; }'
Maybe this is program field 'com.facebook.stetho.R$attr { int icon; }'
Maybe this is program field 'com.facebook.stetho.R$id { int icon; }'
Maybe this is program field 'com.facebook.stetho.okhttp3.R$attr { int icon; }'
Maybe this is program field 'com.facebook.stetho.okhttp3.R$id { int icon; }'
Maybe this is program field 'com.futurice.freesound.R$attr { int icon; }'
Maybe this is program field 'com.futurice.freesound.R$id { int icon; }'
Maybe this is library field 'android.R$attr { int icon; }'
Maybe this is library field 'android.R$id { int icon; }'
Maybe this is library field 'android.app.LauncherActivity$ListItem { android.graphics.drawable.Drawable icon; }'
Maybe this is library field 'android.app.Notification { int icon; }'
Maybe this is library field 'android.app.Notification$Action { int icon; }'
Maybe this is library field 'android.appwidget.AppWidgetProviderInfo { int icon; }'
Maybe this is library field 'android.content.pm.PackageItemInfo { int icon; }'
Maybe this is library field 'android.content.pm.ResolveInfo { int icon; }'
Maybe this is library field 'android.inputmethodservice.Keyboard$Key { android.graphics.drawable.Drawable icon; }'
Maybe this is library field 'android.speech.tts.TextToSpeech$EngineInfo { int icon; }'
Note: android.support.v4.app.NotificationCompatJellybean accesses a declared field 'title' dynamically
Maybe this is program field 'android.support.design.R$attr { int title; }'
Maybe this is program field 'android.support.design.R$id { int title; }'
Maybe this is program field 'android.support.v4.app.NotificationCompat$Action { java.lang.CharSequence title; }'
Maybe this is program field 'android.support.v7.appcompat.R$attr { int title; }'
Maybe this is program field 'android.support.v7.appcompat.R$id { int title; }'
Maybe this is program field 'com.facebook.stetho.R$attr { int title; }'
Maybe this is program field 'com.facebook.stetho.R$id { int title; }'
Maybe this is program field 'com.facebook.stetho.inspector.protocol.module.HeapProfiler$ProfileHeader { java.lang.String title; }'
Maybe this is program field 'com.facebook.stetho.inspector.protocol.module.Profiler$ProfileHeader { java.lang.String title; }'
Maybe this is program field 'com.facebook.stetho.okhttp3.R$attr { int title; }'
Maybe this is program field 'com.facebook.stetho.okhttp3.R$id { int title; }'
Maybe this is program field 'com.futurice.freesound.R$attr { int title; }'
Maybe this is program field 'com.futurice.freesound.R$id { int title; }'
Maybe this is library field 'android.R$attr { int title; }'
Maybe this is library field 'android.R$id { int title; }'
Maybe this is library field 'android.app.Notification$Action { java.lang.CharSequence title; }'
Maybe this is library field 'android.preference.PreferenceActivity$Header { java.lang.CharSequence title; }'
Note: android.support.v4.app.NotificationCompatJellybean accesses a declared field 'actionIntent' dynamically
Maybe this is program field 'android.support.v4.app.NotificationCompat$Action { android.app.PendingIntent actionIntent; }'
Maybe this is library field 'android.app.Notification$Action { android.app.PendingIntent actionIntent; }'
Note: com.google.android.gms.internal.zzanx accesses a declared field 'theUnsafe' dynamically
Note: com.google.android.gms.internal.zzsb accesses a declared field 'MODULE_ID' dynamically
Maybe this is program field 'com.google.android.gms.dynamite.descriptors.com.google.android.gms.flags.ModuleDescriptor { java.lang.String MODULE_ID; }'
Note: com.google.android.gms.internal.zzsb accesses a declared field 'MODULE_VERSION' dynamically
Maybe this is program field 'com.google.android.gms.dynamite.descriptors.com.google.android.gms.flags.ModuleDescriptor { int MODULE_VERSION; }'
Note: com.google.gson.internal.UnsafeAllocator accesses a declared field 'theUnsafe' dynamically
Note: the configuration keeps the entry point 'com.google.android.gms.flags.impl.FlagProviderImpl { void init(com.google.android.gms.dynamic.zzd); }', but not the descriptor class 'com.google.android.gms.dynamic.zzd'
Note: the configuration keeps the entry point 'com.google.firebase.crash.FirebaseCrash { com.google.firebase.crash.FirebaseCrash getInstance(com.google.firebase.FirebaseApp); }', but not the descriptor class 'com.google.firebase.FirebaseApp'
Note: the configuration keeps the entry point 'com.google.firebase.iid.FirebaseInstanceId { com.google.firebase.iid.FirebaseInstanceId getInstance(com.google.firebase.FirebaseApp); }', but not the descriptor class 'com.google.firebase.FirebaseApp'
Note: there were 7 references to unknown classes.
You should check your configuration for typos.
(http://proguard.sourceforge.net/manual/troubleshooting.html#unknownclass)
Note: there were 3 classes trying to access enclosing classes using reflection.
You should consider keeping the inner classes attributes
(using '-keepattributes InnerClasses').
(http://proguard.sourceforge.net/manual/troubleshooting.html#attributes)
Note: there were 3 unkept descriptor classes in kept class members.
You should consider explicitly keeping the mentioned classes
(using '-keep').
(http://proguard.sourceforge.net/manual/troubleshooting.html#descriptorclass)
Note: there were 17 unresolved dynamic references to classes or interfaces.
You should check if you need to specify additional program jars.
(http://proguard.sourceforge.net/manual/troubleshooting.html#dynamicalclass)
Note: there were 7 accesses to class members by means of introspection.
You should consider explicitly keeping the mentioned class members
(using '-keep' or '-keepclassmembers').
(http://proguard.sourceforge.net/manual/troubleshooting.html#dynamicalclassmember)
I checked the ProGuard rules in app/proguard-rules and I noticed that there are ProGuard files for OkHttp2 and RxJava (1), while the dependencies list OkHttp3 and RxJava2.
Build fails when trying trying to deploy the 'release' flavor. Apparently the ProGuard files are not up to date.