I've been making ciabatta for several years now, using a recipe I got here. Pre-ferment, knead with dough hook in a Kitchenaid mixer, French fold twice, shape, rise, slash, bake. The usual :)
After all this time, I think I've finally mastered the recipe. All too often my bread turned out dry and flat, without much in the way of holes.
Problem one, I was letting it over-rise. I'd start a rise, go back to the computer, forget about the bread, realize with a start that I'd forgotten it, and find it climbing out of the bowl. I set a timer now. 1 hour between stretch and folds, 1 hour to rise after shaping. I'll cut that by a few minutes if it's particularly hot and humid here in Honolulu. I know that you should trust the bread, not the clock, but I forget the bread if the timer isn't beeping.
Problem two, I wasn't letting the pre-ferment go long enough. 16-18 hours is better than 12 (for me at least).
Problem three, I wasn't aggressive enough with the hydration. I get tender, delicious bread, with large holes, ONLY if I push the hydration to the point that the dough is almost impossible to handle. When I knead it with the dough hook, it should ball up around the hook, but stay stuck to the bottom of the bowl. When I turn off the mixer, it should slump back into the bowl. Forming it into a ball and oiling it for the first rise is challenging. After that, as the gluten develops, it gets easier to handle.
Bread would be better if I raised it in a banneton and used a peel to slide it onto stone or tile, but it's OK as it is. I let it rise on an old baking sheet, without any support.
I wish I had a camera to show you the results. Finally, boastable bread. Only took a few years.