We've released a hotfix for 1.2 that we hope will address most of the issues you have been having!

Changelog

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####################### VERSION 1.2.1 ########################
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# Features
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* Forming a Defensive Pact now cancels guarantees and non-aggression pacts with that country
* Primitives nuking themselves now properly affects pop count
* Risk of Malcontent Slaves faction effect "Interstellar Railroad" now scales from 1% to 5% risk with 5 to 11+ owned slaves, down from 2-10% risk with 4-8+ slaves

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# Balance
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* Upgraded Nomads arsenal and ship designs. Reduced Nomad Fleet HP and damage bonus modifier from +50% to +25%. Overall they should be stronger than before
* Reduced HP of Nomad ark ships and gave them basic weapons

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# AI
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* Fixed AI not properly signing white peace in some wars that would just drag on forever
* Fixed AI not declaring prepared wars
* Fixed a case where sectors could get stuck due to lack of energy tiles and respect tile resources
* Multiple fixes for AI combat behaviour

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# User Interface
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* Fixed spelling in English localization for Attitude Map Mode

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# Bugfixes
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* Fixed a bug where merging fleets would prioritize the smallest fleet
* Fixed a bug where Gaia world spawn chance was not explicitly reduced for inhospitable stars
* Fixed issues with democratic elections alternative parties, issue caused the alternative parties to be invalid
* Fixed a bug where the display height of a galactic object wasn't being restored after loading a savegame
* Fixed so that democratic elections check the correct policy flags
* Fixed Xeno Integration tech weights
* Fixed upgrade arrow incorrectly displayed as greyed out for certain buildings on non-capital planets
* Fixed a bug where migration pacts between subjects and overlord were not allowed
* Fixed AI sometimes initiating a vote to kick right after a new member joins the alliance
* Fixed max trust not being properly set to 100 when forming an alliance
* Fixed issue with Nomads building too many new ships
* Fixed issue with Nomads not setting an end point for their journey when playing in a tiny galaxy
* Technology database patches tech_repeatable_improved_core_planet_cap -> tech_repeatable_improved_core_system_cap if save file version is below "Stellaris v1.2.0"
* Fixed CTD due to invalid pops on planet
* No longer wait for research in ALL tech areas to be halted before updating technology research alternatives
* Survey fleet order checks if fleet can move to system, so players can no longer reach out-of-reach systems using fleet view survey button

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# Graphics
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* Improved skybox quality