I am using the desktop free Qlik Sense for testing, I faced this issue a couple of times. I create an app, upload my data and start creating charts after I save and login later, all my charts are gone, the sheet is blank and I cant even edit it or add new charts. The data is still there, so is my story line and even the sheet thumbnail has the layout of my charts. I end up deleting it and creating a new sheet.
