For the last several years I have been baking focaccio using Peter Reinhart's recipe (with some modifiations). The result has been uniformly excellent, until yesterday. Yesterday's focaccia was terrible; and I have no idea what went wrong.

Here's the scenario:
I make the focaccio in 3 stages: first a pre-ferment, then a shaping and an overnight rise in the refrigerator; finally, the topping and final rise, and the baking. I start off with 325g of flour; use some in the pre-ferment; add the remainder the next day; then allow it to rise for an hour. At that point I divide the dough in half, and store half in the freezer.

This is what I did with the latest attempt. I made the focaccio 2 weeks ago, used half (it was delicious) and stored half. Yesterday I took the second half from the freezer, allowed it to come to room temperature; stretched and oiled it, and put it into the refrigerator overnight. Yesterday I took it out, allowed it to come to room temperature, put toppings on it, allowed it to rise, and then baked it. It was awful!! There was no oven-spring; the dough never appeared to rise; and, when baked did not cook properly. One could still taste the flour, and there was no crumb.

My question is: What happened? Why was the first half excellent, and the second half terrible? How did all the yeast die (if that's what happened)?

Insights will be welcomed.
Tom