Sadly on 4.20 I have visibility issues (Android only and seemingly 4.20 only).
Running 4.21 in Android Studio it looks like this is a permissions issue:
02-18 11:26:31.422 16331-16331/com.MatchyMaximus.Matchoo E/PermissionFragment: Cannot launch PermissionFragment:Can not perform this action after onSaveInstanceState
java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
at android.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1877)
at android.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1900)
at android.app.BackStackRecord.commitInternal(BackStackRecord.java:688)
at android.app.BackStackRecord.commit(BackStackRecord.java:646)
at com.google.vr.sdk.samples.permission.PermissionFragment.getInstance(PermissionFragment.java:29)
at com.google.vr.sdk.samples.permission.PermissionHelper$1.run(PermissionHelper.java:62)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6680)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
The especially odd thing was once again with a fresh build (new Engine source from git, etc) I get into the app the first time and then it fails on subsequent builds.