First of all, the mother cat may eat some or all of the kittens because of some problems at birth, such as reproductive diseases or chromosomal abnormalities. The mother cat could feel the problem and decided not to let these kittens live.
Secondly, the mother cat may not have enough resources to take care of all the kittens born, such as enough milk or space. In this case, the mother cat may "carefully select" which kittens can stay until they are strong and healthy enough, or the mother cat has enough resources to feed them.
Another possibility is that the mother cat did not socialize properly before being taken away, which led to her lack of protective instinct for her kitten. In this case, the mother cat may eat the cub within a few hours after the first delivery, which is very unusual.
No matter what causes the mother cat to eat kittens, this behavior needs the professional help and advice of pet doctors and pet experts. Experienced pet doctors can help diagnose the problems of female cats and provide necessary treatment suggestions and methods. Using contraception or sterilization on female cats may prevent this from happening.