This happens in 1.11. I haven’t tried 1.12 yet but I don’t see anything about it in the notes. Sometimes my ships will go off the viewable screen; I have only noticed this happening on the bottom.
I noticed that the highlighted area of the map (in the lower left) can be moved so that it touches the left and top sides but it cannot be moved to touch the right or bottom sides. Possibly that has something to do with it?
i have only noticed that in 1.12. but it wont cause any serious problems, enemy ships tend to return and die honorably
It doesn’t cause any problems, they carry on the fight normally, it’s just that you can’t see them sometimes.
Ive never had a ship go fully off the viewable screen, but Ive had them up at the top edge so I cant see the whole ship.
I’ve had whole ships go off, for many releases now. I think frigates are the right size to completely disappear off screen.
Ah well, that’ll be why Ive not seen it. I hardly use frigates 
I only noticed them going off the screen in 1.12. Before that, they were piling up against the walls and getting stuck in the corners.
I agree, it’s not getting in the way too badly, though it is kind of saddening to be watching and ship and then have it disappear off the side of the screen. Thankfully, they’ve always come back.