How to get DS to take a bottle at 10 again?

DS is 6m old. He used to have a bottle at 10 which from 4m saw him through. He started weaning at 17w and slept through until about 4 weeks ago. He is now on 3 meals a day plus formula. He is at my parents Mon, Weds and Fri and nursery Tues and Thurs. My parents have tried to replicate nurserys routine so breakfast at 830, dinner at 1130 and "tea" at 330. We were then giving him another meal with us at our teatime. We changed this to be just a small bowl of porridge to see if this helped with his 10pm bottle feed. Nope. Still doesnt take anything. Ive even tried not giving him tea at our teatime. Nope.

He clearly needs something as he has started to wake up at  and draining a whole 6oz bottle of milk.

Any suggestions? TIA x