This is a short story about a AI controlled transport starship that suffered from an accident and becomes lost in interstellar (intergalactic?) space in such a way that it would take a prohibitively long time to return to civilization.
The ship in its despair moves further into the emptiness and discovers another lost ship(s) there gathering mass as a hobby, to pass the time? It then takes over this task with an unremembered goal behind it.
That's as much as I can remember about it and many searches have been fruitless. The story itself was discovered once in a 'Top science fiction/speculative fiction short stories' type list in a lost thread somewhere.
Edit: This was read sometime in the last year as a part of a list of new or lesser known SF short stories online. I think I saw in a post on /r/printSF which I can't seem to find regardless of how I word my search terms.
Night Watch sounds familiar but I recall the collection of mass was a key part and have no memory of any crew.