Often when working in QGIS print-composer (2.14 and prior), at a certain point the map content disappears and only the empty map frame remains. This happens mostly after closing and re-opening my project or randomly after I hit the "refresh preview" button.
My solution so far was to just add new mapframes (over and over again) but this is annoying.
What is the reason behind my map-preview disappearing and what to do about it? The screenshot shows the problem and the general adjustment I am using.