Rising / Fermentation issue

This is my first post to Fresh Loaf!

I made this recipe twice. The first time, it worked out pretty well, but with the second, I had some trouble getting the dough to rise properly.

800 grams of flour: 80% White bread flour; 20% Whole Wheat. 90% hydration (including 50 g olive oil) . 2% instant yeast; 1.5% salt. (This is rather high hydration; I was experimenting in order to try for a more open crumb.)

1. Preferment - a Poolish made with 50% of the flour (including 100% of the Whole Wheat) and 50% of the water and 1 g of yeast. About 12 hours.
2. Autolyse in the AM with remaining flour and water for 1 hour. (room temp is about 21 C)
3. Mix in oil and yeast. Wait 30 min then add salt. 
4. Mix and stretch dough in the bowl 4 times @ 10-min intervals. 
5. Stretch and fold 4 times at 30 or 40 minute intervals. 
6. Ferment until doubled and fluffy - about 2.5 hours. 
7. Pre-shape. Bench rest about 30 min.
8. Shape and place in banneton. Rest about 1.5 hours.
9. Bake at 230 C. for 30 min. 

This loaf turned out well -- except that the oven rise wasn't particularly great and the crumb not as open as I was expecting.  I decided that next time, I would try also some kneading in addition to stretching and folding. 

The second time, one difference was the autolyse. My wife informed me she wanted to go out for the day just after I combined the rest of the flour and water, and so I had to let the dough autolyse for 8 hours. Even though the dough had just one gram of yeast from the preferment, after 8 hours of autolyse, the dough had risen quite a lot - almost doubled. Another difference from the first bake was that I added the other ingredients and started the fermentation late in the afternoon - in a rather cool kitchen -- about 18 C. During the mixing and stretching the dough acted normally, starting to strengthen after each 10-minute interval. Then I started doing some kneading, using the slap and fold technique. But weirdly, after strengthening a bit, the dough fell apart, turning to goop. I gave it intervals of 30-minutes between stretching and then slap and folding, but each time, the dough remained goopy. Then I decided to just go "no knead" and put the dough inside the microwave with a cup of hot water (i.e. a temperature of around 23 C). After two hours, not much had changed and I decided I would leave the dough to sit overnight. But now I was concerned about over-proofing, so I put the container outside in the night air, which was around 6 C. The next morning the dough had risen about 1/3 and looked fluffier than before. I brought it inside and let it continue to ferment for about 4.5 hours. At this point it had risen about 2/3 (i.e. not doubled) and even had some large air bubbles. I then pre-shaped and baked as above. 

Though the loaf flattened a bit after removing it from the banneton, it baked OK. Oven rise was minimal - but the texture of the crumb was chewy and more open than the week before. So the bread was not a failure by any means. I really would like to know why the kneading caused the dough to get gloopy rather than tighten. Was it the cold temperature? Slap and folding a high-hydration dough? The long autolyse? 

Thank you!