Thanks Paul,
Another Stencyl developer using Facebook told me this 1 year ago, but he solved it at the end. Didn't told me how. Maybe he had to prove that the app is working, as you did.
Anyway, this is a thing that happens to Stencyl games and i wrote also to Stencyl stuff if they can wide-support Android APK Stencyl on simulators on MacOS.
What this means:
ON MACOS - Testing APK in simulators
OjyaLeaderboard for Stencyl using MACOS and different simulators Android AVD, Bluestacks gives the BLACK-SCREEN but the game is fully functional.
OjyaLeaderboard for Unity3D works great on all Android simulators on MACOS.
You can solve how? RUNNING Bluestacks,Andyroid or Android AVD using Windows-Parallels or any virtualisation in MACOS.
So this is a Stencyl issue known. So you have to use real devices or use the above method.
ON WINDOWS - Testing APK in simulators
Stencyl - OjyaLeaderboard works on windows android simulators with no problem.
ANSWER: A big number of facebook reviewers, and this is a confirmed information, are using MACs with Android Simulators.
Stencyl APK games unfortunately have this issue(black screen), instead other game engines, like Unity3D, are not having this problem with their APK games.
For Facebook app review the game developer must specify to test the game on windows OS using android simulators or at real devices, but not on MacOS.
Screenshots below: OjyaLeaderboard Stencyl(black screen) with Bluestacks on MacOS -issue
OjyaLeaderboard Unity3D , using Bluestacks on MacOS - works
OjyaLeaderboard Stencyl using Bluestacks in Parallels-Windows - works