Dough volume shrinking during the cold retard
Does any of you experience the dough volume shrinking after putting it in the fridge for the cold retard?
I am using an 80% hydration recipe with 40% whole wheat flour and the rest, strong wheat flour. Innoculation 20%.
I noticed this as I used an aliquot jar. After the bulk fermentation, the aliquot jar indicated 75% increase and after 5 hours in the fridge went down to 50%. I tested the same recipe also with an increase of 50% and again, in the fridge went back to 25%.
The next day, while opening the fridge door few times during the day, the dough starts to rise again and reaches actually the initial level, but during the night, it remains constant.
There is no issue with the baked bread and actually, I am very happy with the result: airy crumb, perfect ear.
I would like to understand why is this happening and what would be the cause of it, as it did not happen with many recipes I tested before.