Discussion from Discord (kevin the alarm clock is me for… reasons)
[1:43 PM] kevin the alarm clock: the lines with "occurrences" look like
"occurrences" : [1, 1],
[1:43 PM] kevin the alarm clock: that first number is the important one
[1:43 PM] kevin the alarm clock: that number is the number of mandatory instances of that special
[1:48 PM] kevin the alarm clock: for example, Urban Development is adding 40 buildings as mandatory, but NONE of those are the target of a mission
[1:49 PM] kevin the alarm clock: that's literally half of the problem
[1:50 PM] kevin the alarm clock: if you go through and change those lines to be
"occurrences" : [0, x],
where x is whatever is there now, it should just start working
[1:51 PM] kevin the alarm clock: the only exception to this kind of thing is when a special is a target of a mission, so you have to have one otherwise mission creation will fail
[1:52 PM] kevin the alarm clock: I think what we are going to do is remove the ability to set that minimum, and instead build a list of mandatory specials by enumerating them in the missions themselves
[1:54 PM] Curt: I won't be fiddling with any of the code myself, but good to know a solution is in the pipeline. Thanks, man.
[1:55 PM] kevin the alarm clock: meanwhile just set a bunch of those numbers to 0 and it'll start working
[1:55 PM] Curt: 
[1:56 PM] kevin the alarm clock: I'd start with Urban Development, More Locations, More Buildings and Extended Buildings
[1:56 PM] kevin the alarm clock: I'm 99% sure those don't have missions targeting them
TL;DR Find the “occurrecnces” fields, and change the first of the two numbers to 0, and it should resolve your issue.
Target the “more buildings” mods, since they cause most of the problem.