Why is my baguette type bread coming out almost flat? I bake bread almost every day.  Mostly French baguettes, old stretch and fold every 45 mts. method for 1st proofing, couche for 2nd rise. Make sourdough too.  But my bread loaves, which were coming out very good, but wanted to make better, are now (last two weeks) coming out almost totally flat when out of the oven (oven temp ok).  They actually look nice and fluffy (Too &quot;marshmallowy&quot;) after 1.5-2 hrs. proofing on top of counter on tray covered by dry towel.  Used to proof for 1.5 hrs. but the 2 hrs. gave a nicer, puffier (but soft) look.
What happens:

So, when I score the bread, simple center cut, it starts to deflate a little.  I bake it with plenty of steam yet no oven spring, it's FLAT! BUT...the taste is great, only has little crumb but it's NOT DENSE...

What I've tried:

I use plenty of steam with pot in bottom of oven and boiling water, lightly spray the loaves.

I am pre-preparing everything (this is new, could it matter?), including sifting flours (half AP/half bread) the night before, the rest in separate containers.

This bread uses a 24 hr. poolish, which is was checked and it's fine.


QUESTION:

How can I proof for 2nd rise if I can't use my oven, which is being heated?

I have tried keeping it in the oven until last minute, finish proofing on top of counter (cooler temperature) in order to preheat oven for baking the change in temp seams to start to deflate dough.

How can I tell that the dough is ready for baking and proofed enough? (tips!) I tried poking it, but just left a hole in the formed &quot;baguette&quot; shaped loaf which didn't spring back at all.  Felt marshmallowy:(  When ready to bake is it supposed to feel firm or very soft?

Is there a chance I could have OVER-kneaded the dough in my KitchenAid? I mix for 2 min. in speed 1 and up to 7 min. in (varies) speeds 2 and 4. (Recipe calls for 2 min mixing and 3 min. on speed 2) I have been kneading say about 3 min. on 2 and 4 on speed 4.  Then I manually knead for about 10 min. (not too hard).


My house is coolish, 70 degrees, open kitchen.  I can't afford a proofing box.  All other breads proof and bake perfectly well.  None of them use the stand mixer (!) Only this one has given me problems.  I have also tried different recipes, same problem - but it seems to work for everybody else. Please help? Thanks and stay safe!:)
If you haven't changed your recipe then the problem is in your method, and it sounds like you are over proofing. If your bread expands too much in the final rise it gets over-extended and tends to collapse when scored, exactly as you describe. It's easy to 'get greedy' and try to eke out that much more expansion, but it's actually a very common mistake.
Reduce your final rise after shaping and you'll get a better result.  Go for a doubling in size typically, maybe a bit more. It's hard to give a time on that, but typically 1.5 hours is the most I'd give it, I like to still have some visible rising going on when I put it in the oven because part of oven spring comes from the yeast.
If you do over-prove it's not a disaster, just don't score it, then put it into the oven gently.
As for how to proof the dough, you don't need to use the oven, in fact I'd recommend against that unless your house is really cold. 70°f is fine for proofing, it just takes a bit longer than a warm oven, and you often get more flavor and better structure if you don't rush it. One thing I would suggest is not to use a damp towel as the weight of it on a small baguette can hold it down a bit, and the evaporation of water from the towel cools the bread and slows down proofing. Instead proof your bread in a clear plastic bag (clear so you can see through it, no other reason). You blow air into the bag and then clip it, the air will keep the bag from contacting the dough and sticking. The bag will seal in the heat generated from the yeast activity as well as keeping in moisture, preventing it from forming a skin.