My chefs keep on saying “survivors cannot work due to insufficient raw materials” what is that?

"insufficient raw materials" means your chef doesn't have enough meat to make meals. if you can, upgrade your hunter cabin or other buildings to get enough materials to upgrade hunter cabin. then the hunters will be able to bring back more meat for meals.

"sick worker" you'll need a hospital. there will be an assigned hero for this building. upgrade her and the building and your workers won't die as often, if at all.

If one production build relies on a resource from another building (i.e. The foundry relies on coal) and there is not enough of it being produced then it will slow down or stop the secondary production. When it slows down then the workers will stop working one at a time to only use what is coming in.

You can tap on the Statistics option (the pie chart icon on the right) to see an over view and production chain list of what you are producing and see what items you don't have enough of.

If it is the chefs in the kitchen saying it then you need to increase production of the raw food, this will be by improving the hunters cabin, or other food production building.