Why does the canteen says no prisoners assigned

I managed to meet the requirements to feed all prisoners. Much of it is luck, due to the goal requiring you to literally FEED all prisoners, and not all prisoners will be hungry at the same time.

The To-Do list has three icons for the prisoners:

• Red icons for hungry prisoners. If you have a psychologist, I believe this is roughly when their "Food" need is almost full.
• Green Dots indicate prisoners currently eating. This will only happen during Eat activities.
• Green icons are prisoners that are not currently hungry. They will most likely NOT eat during your Eat activity.

Under the prisoners, you see the Meals "bar" (for lack of a better word). That shows how many prisoners you can feed with the food currently on the Serving Tables. Note that that does not take into account food on Cookers or currently in transit to the Serving Tables.

The simplest way to actually feed all prisoners would be to limit the Eat activity to once a day. Doing so, and ensuring you have enough Cooks to make enough food, will ensure you can serve up the maximum amount of that gourmet jail slop.

Note that there isn't actually any reward for being able to feed all your prisoners; it just seems to be an indicator of your prison's current hunger state.

You can try to fix the next intake problem and see if that resolves the food deliveries (it's not going to deliver food when there are no prisoners to eat it).

Find your save game file and open it in a text editor. in the top section of the file you are looking for two values TimeIndex and Intake.next; edit the Intake.next value to be 100 more than TimeIndex. That should resolve the time to next intake issue.

Reload the save game and see, after the new prisoners have arrived, if you start to receive food deliveries again.