There's just no real way to know for sure what happened.
We had one boer doe, bought "exposed" due in Jan. I had at one point thrown our 'clean up buck' in the pen w/ all the does many months after I got her. So she goes into labor one night in early January, I wait w/ her and all I see her pass is just tons of red fluid, and I mean bucket fulls. This was years ago when we were still fairly new to kidding, but I knew something wasn't right.
I thought she was 'due' and couldn't get the kids out, so I called the vet. She comes, knocks her out, does a C section and....pulls out this small (no way near full term) uterus, feels around, and...nada. Nooo kids.
Even the vet is confused so we go looking around in all the places she'd squatted and passed all the fluid and find 3 - 6" long (roughly 60 day) fetuses.
Turns out she wasn't bred when I got her, our clean up buck had gotten her.
Vet's best guess was placental previa, fluid build up caused the doe to look huge / due, and when she finally passed all the fluid / kids she was fine.
Our vet still laughs about the 'only time she ever did a C section on a doe who WASN'T pregnant....
The point of the story...sometimes a doe who looks hugely pregnant can lose the kids w/ out you realizing it.
If I hadn't been there and seen her passing all that fluid that night, I'd never have had a clue what really happened.
There's also something called a "cloudburst," which is where the doe appears to be bred and can go through a complete pregnancy cycle...just without kids. At delivery, she delivers water, hence the term..