I have a sneaking feeling that your prisoners are in lockdown because there's an external breach to the prison, like a gap in a wall or an open door. This will essentially force them to stay in handcuffs in their cells, without being fully assigned to that cell, which will also make a canteen not work (it will normally say there are no inmates assigned). Either that or you've made the area outside the cells staff only so the inmates can't walk over it. Can you check see whether it's either of those and let me know?
Nat D11
