Sims 2 Legacy Collection - Sims disappear after finishing University

I played with Stella Terrano, she is a pre-made alien college student at La Fiesta Tech.
I was able to move back to Strangetown with her. But her children disappear after finishing University and moving back to the town.

I tried it with another pre-made college students on different Universities, precisely the same occurs. They can move back to town where they are from but their children disappear when they move back from the Uni.