Re: Problem with app developed with Qlik 12 and Server 11
First, I would immediately restore a backup of the installation before touching JS files if you want to have Qlik Support.
Second, developing in one version and publishing in another is not supported. It can work, but it is not supported: try to open the app with Desktop 11.20 (same SR than the server) and confirm whether the issue keeps happening. If it does, contact Qlik Support attaching a sample of your app.