Check fermentation and dough strength before changing several things at once. Overproofing can produce a slumped loaf, while the flour and gluten structure affect support. Spreading alone cannot tell you which factor caused this batch.
Record the bake
Write down flour, water, starter amount, room temperature, fermentation times and how the dough handled before shaping. Photograph it before and after turning out. A recipe's clock is a reference, not proof that your dough reached the same stage.
Look at fermentation
King Arthur notes that overly active starter can accelerate fermentation and lead to overproofing. If the dough became very fragile late in the process, compare an earlier bake point next time rather than assuming it needed a longer rise.
Review structure and handling
Gluten supports the gas in bread dough. Compare your flour and water amounts with a tested recipe, and review its mixing and shaping method. Do not assume every wet or spreading dough needs the same correction.
Change one variable next time
Keep a baseline recipe and make one recorded adjustment. Compare loaf shape and crumb, then bring the recipe, timing and photos to a baking discussion. This is a troubleshooting sequence, not a diagnosis of an unseen loaf.
Sources and further reading
These are general starting points, not a diagnosis or a verified account of your circumstances. Related discussions offer perspectives; prepared contributions are not independent evidence.