First time, I had just started a space "kill x number of ships/patrols", I had a power outage, lost connection. When I logged back in, and chose to "continue mission", the area looked the same but no enemy to fight. I went back several times over the next couple of days...same thing.
Second time is was a ground "kill x number of patrols.." about 1/2 way through, I had to log out (wife argo), I logged back in later in the day, I started in space and had the option to continue. Again, same area, but no enemy to fight.