If you've managed people, these are all familiar problems. I found you need much more than a functional specification, you also need motivation, background, related work, ideas tried, etc., because those help disambiguate the right path in the inevitable situation where your original task description is unclear or conflicts with itself.
Yes I'm using the entire consultancy stack - define values, etc, and work your way down the "where do these not match reality on the ground and need change", but for little robot people instead of (arguably less messy) humans.