The word fallaban is the imperfect form of fallar in the third person plural.
See the full fallar conjugation

fallar

La industria y los transportes fallaban constantemente ante las exigencias concentradas de los tiempos de guerra.
Industry and transport continually revealed their bankruptcy before the concentrated demands of wartime.
Si ellos vivían conforme a la Ley, recibirían la salvación; si fallaban en vivir según la Ley, no recibirían salvación.
If they lived by the Law, they would receive salvation; if they failed to live by the Law, they would not receive salvation.
Por otro lado, cuando les sugería estudiar del Libro Básico provisto (y traducido) por Wizards para iniciar a los jugadores, fallaban miserablemente en el examen escrito.
On the other hand, when I suggested them to study on the nimble Basic Rulebook provided (and translated) by Wizards for starting players, I had them fail miserably on the written test.
Estos sujetos bebiendo té con azúcar escribían en sus bitácoras tratando de hacer funcionar esto, con estos 2.600 tubos de vacío que fallaban la mitad del tiempo.
Those guys drinking all the tea with sugar in it were writing in their logbooks, trying to get this thing to work, with all these 2,600 vacuum tubes that failed half the time.
De ese modo sobrevivían o fallaban juntas, o sea que si una comunidad era muy exitosa todos los individuos de esa comunidad se replicaban más y eran favorecidos por la evolución.
So they survived or they failed together, which means that if a community was very successful, all the individuals in that community were repeated more and they were favored by evolution.
Y nunca acertaban, siempre fallaban de formas divertidísimas en su optimismo.
And they're always wrong, always hilariously, optimistically wrong.
Mis relaciones se deterioraban o fallaban.
My relationships were fraying or failing.
Anteriormente, la cooperación entre los tribunales y el ministerio competente había sido insuficiente, por lo cual los reglamentos fallaban en la comprensión de los tribunales, la organización interna, los lugares de trabajo y los elementos que los determinan.
This was very important as the study of past practices revealed that cooperation between courts and the competent Ministry had been insufficient and resulted in a number of Rules shortcomings with respect to the understanding of courts' internal organization, workplaces and the elements determining them.
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