2 reasons usually 1 is she miscarries to make room for another litter that she has inside her,or 2 if shes been stressed like tank maintenance or moved from one tank to another for example don't worry she,ll be fine my guppies did the same
ive got my black one in a breeding tank, and the rest of my mollies died.
the breeding tank is the one with the v insert and the white mollie is hanging around the tank
OK lets start again.lets find out why your mollys are dieing,do you add salt to there water?.in what way did they die,i suggest if you want babies get more female mollys so he'll chase other fish and it will give her a break. then when one is pregnant wait till she get really large eventually she will look like she is gonna pop and she will try to hide away that's the time to put her in a breeding trap,if you do it before it will stress her and she will miscarry them