I'm on city 7. My kitchen is maxed and my greenhouse is maxed. My hero is at level 50 so providing..

Make sure the table to eat is maximised. Like the top and bottom column of the kitchen are both at max

Mine is doing the same thing. Both levels in the kitchen are maxed, and my hero is on 50. My survivors only eat for like 2 seconds and don't get full even though there's 109k meat. And feeding time runs out before they finish although they are moving at light speed. I think it's a glitch.