I am playing Extended AI Improvement Mod 1.05 no pirates, 800k research, harsh start for me and agreeable for AI, extreme difficulty, sparse indy and colony, 1.5 sector colony range.
Playing Kiadian Republic, colonised a fairly remote marshy planet with Kiadian 30M with civs using fairly slow gerax hyperdrives and later discovered a Sluken insectoid indy several sectors away. Civilian passenger ships carried many Sluken migrants to the marshy planet until they outnumbered Kiadians and other indy races and then were dissatisfied and stopped paying taxes because they have racial antipathy of -23 for Kiadian which dominated the planet stats and the planet only got +7 for development. +77% leader and governor happiness bonus adds one point because they % is on a low number to start with.
I tried to build a station to add medical and recreation and it wont even build.
I find this does not ring true. If they were conquered or enslaved Sluken it would be justified but they are not, they migrated from an indy at their expense and of their own freewill, like a new immigrant to the USA for example. They would be optimistic and adjusted to the empire they chose to join not fomenting rebellion based on speciesist rage.
This mechanic is unsatisfactory and that is the modders' responsibility, FYI the antipathy numbers are imbalanced and much too negative, they only make sense in the context of conquest (where they are offset by existing development), and are at their most punitive in the context of migration which is the context in which they should be least punitive.
This is why I think there needs to be separation of population identities based on their history in a location for DW2, not simple speciesist stereotypes applied across the board. Even if it is unintentional this has the appearance of a racist premise and we should do better.