I know lots of people have this problem. I have had this problem since 2017. still seeing it. Basically every single building I click on has only 0-3 people working at once. I have no water, because no one is working, and food is falling. Honestly I dont know how the colony is still going with literally maybe 100 people of 27000 working. I'll answer an questions possible while trying to figure out this problem. In the past, ive found that... killing...the whole population works... i dont wanna have to do that this time though.
Heres a link to show whats happening: https://goo.gl/Dtn2Vi
Oumar Diop
If you open the building and click on view workers, it helps for that building.
I think it has to do with colonist virtualization and if you click that, the workers get devirtualized and real people move in.
You see it when you click that building repeatly after that. The stats of workers change.
It's a hassle for a lot of buildings in big colonies, but it may help with your food problem. Need a real fix for it.