Dough sticking/losing structure during/after shaping

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First time trying to make my own bread, I'm certain I did something (or some things) wrong but I'm not sure where.  Please help.  Here's roughly how it went up until proofing.

  1. Created from a starter I created two weeks ago, that is by all accounts mature and healthy.
  2. Following this recipe, but critically had to substitute out the unbleached AP flour for a 50/50 mix of bleached AP flour (Gold Medal)/Caputo 00 flour.  
  3. All went well up until pre-shaping.  Bulk ferment rose about 25% after 4 stretch/fold cycles, had lots of gas bubbles developing, surface looked smooth right before the pre-shaping.  
  4. First tried pre-shaping without any additional flour, just slightly wet hands.  Dough stuck to everything - hands, scraper, work surface.  Could not fold very well, shaped as well as I could into boules and put the under bowls to rest for 30 minutes.
  5. Decided to pre-shape one more time to be safe.  Could not even get the boules off the work surface without leaving a bunch of it stuck to the work surface.  Scraped everything together and combined it back into one big ball and back into the bulk ferment bowl, where I let it sit for another hour hoping it would build up stronger gluten.
  6. Back to pre-shaping, this time I tried flouring - again hands, scraper, work surface.  The flouring helped tremendously to prevent sticking and allowed me to build something resembling tension on the surface and form a decent boule shape.  But after letting it rest 30 minutes and coming back to do the final shaping, I found it again glued to the work surface.  Removing it tore up any structure or shape I built.  
  7. Gave up, made it into somewhat of a boule shape and tossed it into the proofing bowl/towel and into the fridge.

What could cause the dough to be somewhat OK during pre-shaping with flour (not as sticky, builds some surface tension, holds a shape) but fail after resting?  TIA.

Just go with it and get it in a round cake tin, bake at 350 with steam, slashing with an oiled blade the moment before it goes in... cut deepish. It will rise in the oven, then whack the temperature right up for the rest.

I scrunched up some baking paper and put it around the bottom of a round cake tin then put another sheet of paper on top, placing my flour dusted wet mess in, then tensioning the sheet around the base of the tin to help it all keep shape.

Dad-baking style.

I've also been having inconsistent results with that recipe recently as well and my loaves also seem to break down somewhere between the bench rest and final proof. My first 4 batches were great and then the most recent 2-3 have not been so great I've been going back through my notes and trying to figure out what happened. I have a feeling hydration with the flour your using is probably your #1 issue, but in case it's helpful, here's the things I'm noticing and changing about my approach to bread to try to get better, more consistent results:

  1. Flour: When I used King Arthur Bread Flour, I got enough structure in the dough to keep it from turning into a sticky pancake. When I used King Arthur All Purpose or mixed in some spelt as part of the white flour - I got sticky dough that was exceptionally difficult for me to manage. With flour mix you're using, it may just be too much hydration, which leads me to....
  2. Hydration: I'm realizing we don't need 75%+ hydration to make good loaves. I'm going back to 65% and working my way up from there until I get something that's a happy medium for handling and ease of mixing. Check out this post on How to Get an Open Crumb With Stiff Dough . For further proof, in Bread by Hamelman, many of the basic bread recipes are ~65% hydration.
  3. Incorrect proofing temperature for my starter: In my last two attempts loaf, the dough was overly sticky and flattened out a ton when I dumped it out into the dutch oven and slashed it. The crumb on the baked loaf was dense. I have a hunch that the primary issue for me here stems from fermentation temperature....
    • Tartine's recipe says ferment at 78-82*F and my early loaves, I'd just leave the oven light on and it could easily get to 84*F+ in the oven.
    • My last few loaves I've been trying to maintain 76*-78*F during fermentation since I read somewhere yeast like that....
    • My suspicions are that either (A) my starter likes 76-78*F a little too much and my dough simply over proofed or (B) my starter produces some "negative" byproducts at temperatures lower than ~80*F that break down the dough structure before the yeast can produce enough gas to properly rise the loaf.

Hopefully that gives you some helpful things to think about. I'm making up a test loaf today and we'll see how it goes!