
2 years ago one of my girls gave birth to 6 healthy pups, the scan showed the same as yours lots of floating debris, ie. a reabsorbing feotus, she did pass a few small dark clots, which stopped after a couple of weeks, the rest of the pregnancy went to plan. My vet did say that sometimes this could be the start of the whole litter going the same way, so really I don't think there is a definite answer. But as the rest of the litter looked good on scan, I would stay positive.
Good luck.