The reason you are seeing a black screen after your game or app loads in Ludei’s Cocoon is because they don’t allow you to use Cocoon.js which is probably what you relied on for you app itself.  Programs like Construct2 can export a Zip for Ludei Cocoon but you have to be a premium user of Ludei to use their Cocoon.js, and everyone right now is a free user.  They have a form you can fill out on their control panel which you can request access to become a “Premium” member.  I wish apps like Construct2 can notify users of this problem ahead of time.  I recently made a clone of Flappy bird which you can find at Google Playstore