Waking up at night

We put our LO to sleep at 8pm every night... for 4 weeks now, he has been waking up exactly between 10-10:15pm, screaming and crying. Simply inconsolable unless I offer the breast. Thing is, I’m very certain he’s not hungry. We fed him 100g of cereals and offer both breasts (which he diligently empties) before bedtime. His diapers are fresh and the room is slightly chill (20 degrees Celsius).

He sleeps wonderfully without any fuss at 8pm but why is he waking up 2h later every night??

Is anyone out there facing the same issue? What do you do?