New preview mode
BUG in the new CC 2019 Version. Preview mode forces it's way for some reason during use. Screen becomes blank- only a restart brings back document.
Please accept my sincere apology for the inconvenience. Please get in touch with us at any of the other support channels – https://helpx.adobe.com/support.html . Since this is not a generic issue that we can reproduce at our end, we will need someone to look into your machine to figure out what is going on here.