From what I've read it has something to do with a horizon within a black hole event horizon.
Excerpt from: https://en.wikipedia.org/wiki/Cauchy_surface
"The outermost horizon is an event horizon, beyond which information cannot escape, but where the future is still determined from the conditions outside. Inside the inner horizon, the Cauchy horizon, the singularity is visible and to predict the future requires additional data about what comes out of the singularity
I've underlined the part(s) that intrigued me. However I'm no expert and am left wondering if this is just some conjecturing by cosmologists as I see others reject the hypothesis.