Collapsing bread

The last two attempts at my sourdough have resulted in flat bread...I mixed the dough, let it proof for the 12-18 hours. Then when I went to shape it for the final proof, it became much more moist and then wouldn't shape or rise. Just blah. Is it possible if this happens to add more flour and water and let it rise? or will it just remain flat?
Why would it over proof in the first proofing/fermenting? I would like to be able to make consistently good loaves of bread.
Thank you for any insight you can give.
Best Answer
If you are making the traditional type 1 sourdough bread, after the first 12-18h fermentation (stage 1), you need to add more flour and water to refresh the dough (aka backsloping) for 1-2 hours (stage 2). The reason is that by the end of first stage fermentation, sugar in the dough is already been used up by the yeast and lactic acid bacteria (LAB), so dough refreshing is critical to activate the yeast and LAB again. After the second stage, you can shape the dough to the shape you want, and then rest them for another hour before baking. Hope that helps.
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What causes collapsed bread?
Bread that Falls or Collapses Can Be Caused By:If it looks too wet, add flour a tablespoon at a time until it looks as expected. Note that high humidity can add unwanted liquid to a recipe. Not enough salt \u2013 Try increasing the salt by \xbc teaspoon. Not enough flour \u2013 Try increasing the flour by one to two tablespoons.How do I keep my bread from deflating?
Here are 6 ways to stop your bread collapsing and ending up as dense as a brick!What does it mean when bread deflates?
The most common reason for bread deflating after scoring is over-proofed dough. There is a lot of excess gas accumulated in an over-proofed loaf, which is all released when scored. Other reasons include the dough being overly wet and scoring the dough too deep or too shallow.Why Does My Bread Dough Collapse?
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.