600 grams of flour was too much. 400 grams of flour was not enough. This bake uses 500 grams of flour and adjusts the other secondary ratios somewhat.
The recipe uses 250g AP flour and 250g fresh-milled whole wheat flour, (500g flour weight total). 375g water (75% hydration). This time around I cut back on the “other stuff”: it uses 30g each of honey, olive oil, and powdered milk (all are 6% of the total flour weight, the old amounts had been 8%). 10g kosher salt (2% of the flour weight), 1 tsp instant (not rapid-rise) yeast. Bulk rise until doubled then move to the Pullman pan, cover and let rise until 1/2″ from the top of the pan. Bake at 350F, covered for 30 minutes then remove the cover and bake for another 25 minutes or until the loaf reaches 195-200F.
It’s sort of based on King Arthur’s A Smaller Pain De Mie. Or at least it was at the beginning of tinkering.

The newest version uses relatively less honey, olive oil, milk powder, and yeast. This is intended to make the end of the rise a little more predictable and controllable — with the earlier versions there wasn’t a ton of activity for the first 60 to 90 minutes, then things started to happen fast after that.
It should be more manageable but we’ll see how it tastes and ages after a few days. It may be the correct answer will be to restore “other stuff” to the original 8% and just cut back on the yeast and expect the whole pre-bake process to go slower and longer. I feel like it’s getting close to where it should be.
Happy baking