It is not unusual for the doe to still be passingsmall amounts of blood. You may want to try palpating her todetermine if a kit is still being retained. Youwould easily be able to feel the kit as a hard object in the groin area.
We've been breeding Holland Lops for 15 years and found this problem tobe very common at this time of year, however I have been unable to findphysiological data on the exact causes. Our vet could alsooffer no concrete explainations. Possible causes at this timeof year may involve hormones interfering with normal placental andumbilical cord functions or viral/bacterial illness could be to blame.
Birth defects are another common cause of stillbirth as well as manyother possible causes including uterine tumors or infection.
I would rebred the doe (normally done within 3 days of loosing thelitter). It's very possible that the cause was seasonal innature and she may go on to have a successful litter with the nextbreeding.