I found the bug, it is introduced by PK Mod, I’ll point him to the issue. A typo on the minimum city size required (the ‘fat finger syndroma’, you hit 2 keys at once 
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"id": "FEMA Camp",
"overmaps": [
{ "point":[0,0,0], "overmap": "fema"},
{ "point":[1,0,0], "overmap": "fema_entrance"},
{ "point":[2,0,0], "overmap": "fema"},
{ "point":[0,1,0], "overmap": "fema"},
{ "point":[1,1,0], "overmap": "fema"},
{ "point":[2,1,0], "overmap": "fema"},
{ "point":[0,2,0], "overmap": "fema"},
{ "point":[1,2,0], "overmap": "fema"},
{ "point":[2,2,0], "overmap": "fema"}
],
"connections": [
{ "point": [1,-1,0], "terrain": "road" }
],
"locations": [ "wilderness", "swamp" ],
"city_distance": [5, -1],
"city_sizes": [[b]42[/b], 30],