Just made an accidental discovery: I closed SU to work on something else while Enscape was rendering - enscape closed too and didn't complete the render. Can this be changed? Either with a pop-up to ask if you want the rendering to continue or finish rendering before closing.
Also - Why does the render take so long to export? It seems that it is re-generating the image from scratch; can't the current "screen" view be used as a starting point and refined? (Perhaps it already is and I need a better machine.)