Very hard to say really. Was the female big enough to be breeding? Was there any issues of fighting amongst the colony recently? It may have simply been a case of an inexperienced female having a poor first litter. It happens with all sorts of animals that they don't do well with mothering a first time litter.

I'd say to just monitor the situation, make sure there's no reason that female was so stressed she either delivered a poor litter or killed/consumed some of them. When she's pregnant again, see how she does and if she's just a generally poor breeder you might want to consider culling her if another litter fails.

I'm not sure if she could still be pregnant and delaying the rest of the delivery. I know that's possible in some mammals but unsure if ASF's can do this.