Might be that the sector has too many objects for your pc to handle.
Does it do it in other sectors too?
And if you are flying with a big fleet try going to a sector without them following you, does it still do it?
Other than that I can only say run the game, alt tab, press ctrl-alt-delete and see if any of your pc statistics are fully in use. Maybe something is hanging.
If it is the sectors or fleet it would make sense to be limited to your save.