If some land developer wants to build a new arena next to your plot of land - boom you're value just skyrocketed.
If the same land developer backs out of the deal - boom your land is worth less (or is actually worthless).
Your taxes depend on exactly when the assessment was made... and even professionals cannot agree on valuation (as we're seeing in some high profile cases right now).
Even for the same plot of land two people can value it radically differently.
> extremely high vacancies like San Francisco
This is a relatively new phenomenon.
There is no objective valuation for anything really... particularly when it comes to more-or-less unique, speculative properties such as land and/or improvements.
The only reason everyone mostly agrees on, say a car's value is there's a lot of cars exactly like it that have been sold recently in whatever area you are in. Yet, every plot of land is mostly unique and has a tremendous amount of potential, debatable factors when it comes to value.
BuT rEnNoVaTiOnS. Listen, I’m not trying to give you a comprehensive answer. I’m just trying to show that it’s not by far the biggest difficulty, not in the places LVT is most impactful, such as cities with extremely high vacancies like San Francisco.