4 year old sand boa not eating

[Shaiza]

He used to eat perfectly fine. I used to take him out to a separate container to eat f/t and he'd take it right away. Then I moved to leaving it in the cage and it would be gone by morning. Now no matter what I do he's not paying any attention. It's been about 3 months. He doesn't seem to be thin or lethargic. He's quite active at night so I thought maybe he was hungry. Still nothing. I have him on a mix of Aspen and walnut grounds. Heat mat and halogen light. Hot side during the day is around 100-105 and night around 85-95. Never had a problem before so I don't know, just looking for ideas.