12-hour fermentation makes dough wetter
You are overproofing your dough. 2 teaspoons dry yeast, 600g flour and a warm rest of twelve hours sounds like a recipe for disaster to me - not to mention that half of the liquid is milk, which would warrant a closer look into food safety topics as well.

Also, any extended kneading (if used) is usually prior to bulk fermentation, possibly with an autolyse step before adding yeast, but not after a bulk rise. You might choose to "punch down" your dough depending on your desired crumb structure, but kneading renders the previous bulk fermentation moot.

Taking your recipe and environement into account, I would expect your first rise (= double volume) to be complete in under an hour. It seems that due to enzymatic and yeast activity your dough lost its internal structure and the gluten network started to break down. The fact that your dough tends to flow outward, not rise up is another indicator. You can slash and steam as much as you like, once the gluten network broke and the yeast is exhausted, an overprooved dough will not yield good results.

For cold fermentation in the refrigerator the rule of thumb is 1-2% fresh (cake) yeast / 0.33 - 0.66% dry yeast, based on flour weight. For your 600g, that means between 2 and 4 g (or between a generous 1/2 to 1 teaspoon). Use cold ingredients and rest for 8-24 hours. The shorter you want to rest, the higher the yeast ratio, obviously.