Thank you all.
I will reduce the amount of work during those days but add an extra low-intensity day for the lower body to maintain the volume and see how it goes.
If this does not help, I will try to increase the amount of carbs and see if this helps.
Btw, just to make sure it is clear, what surprises me is that my lower-body muscles are not sore at all after the workout. From the second or third set of the main lift however I start to feel without energy, both overall and mentally, to the point that I cannot concentrate properly for at least two hours after the workout.
This seems to suggest to me low glucose levels but I don't see any evident issue with my diet:
I consume 2700 calories per day (few hundreds above maintenance) at 82kg body weight with approx. 300gr of carbs per day (spread almost evenly across the day but slightly higher around the workout time), 160gr of proteins and 80gr of fat.