I just had the following scenario:
I was working in Affinity Designer, created some paths, rasterized them
I wanted to save the rasterized object in a separate file, but didn't really know how to do it.
At some point I ordered to edit it (I thought: the selected object) in Affinity Photo
I realized that it imported the whole document into the Affinity Photo. So I clicked cancel and quit
And then... I realized that Affinity Designer (which was open all the time) no longer holds the document I was working on
if I was more careful I would have noticed what is happening. Still, I think it is bad bad behavior of the program itself if one can trip on it this way and just lose everything.