"No individual obligations" for all vassals

[-Milqart-]

While playing I notice that my vassals do not pay me anything, loading previous saves the same thing happens, but I had much higher income, so the problem appeared recently, but it spread to the whole game even in previous saves.
I see in the screen that all the vassals (except a couple) have the wording "No individual obbligations" and I have not found any reference to this wording.
I removed any mods, which were on a translation and immersive loading screens, nothing relevant.

Is it a mechanic I don't understand, or is it hopelessly bugged?

 

[WTH666444]

You can't continue a 1.15 game on 1.16. Pretty sure the only way to salvage this is both to revert to 1.15 and to continue from a save you never(!) loaded up while on 1.16