I found an interesting paper on the big crunch that may help. It focuses on a non-singular model. In essence, after the big crunch the universe is still something, it doesn’t go out of existence. They’re, of course, setting up an ekpyrotic model. They have an isotropic and anisotropic model. The isotropic has a universe out of control, seemingly, and the anisotropic is very uniform in behavior. I thought it would have been the other way around. What seems to occur after the crunch is that the antigravity, cosmological constant, inverts the universe, ever so briefly, prior to re-expansion. Just like the energy of a rubber band increases when stretched out with the tendency to snap back in on itself so does the antigravity function this way. Why it’s so much shorter when crunched and inverted I don’t know.
The paper: “Antigravity and the big crunch/big bang transition” by Itzhak Bars, Shih-Hung Chen, Paul J. Steinhardt, and Neil Turok