Hi ! The last three attempts with "pain au levain" have proved unsuccessful  loaves because they have not had the desired oven spring. I thought that the flour used is not able to hold more than 70% hydration.

Here is the procedure used to make these breads:

165 grams of leaven (125% h)

400 grams bread flour

50 grams rye

65 grams strong flour

321 grams of water

11 grams of salt

Mix all without the salt, rest for 30 minutes.
Add the salt and the mix Until the gluten is well developed.
First fermentation of 3 hours at 17 º Celsius
Make a "boule" and leave in a banetton for 2 hour of final proof at  21 º Celsius
Bake in a dutch oven at 230 ° C

I've had problems whenever I used hydrations over 70% and a liquid sourdough. It is possible that for some reason the flour does not hold water and the enzymatic action of a ferment liquid and because of this collapse during baking?