From the dev posts on the Steam forums. Will do my best to post these here until the devs append these to the game updates themselves.

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Changelog v1.0.3: ---

Changelog v1.0.4:

Changelog for Stygian Update 1.1.4 (19 December 2019) - Part I:

Add
- Character Profile System
- Quick Save Support
- Tutorial System
- Combat Hit Probability Indicator
- Credits video button to Landing Page

Improve
- Trade sorting algorithm now sorts items by their priorities
- Settings UI have new key binding and tutorial settings
- Nithon object layerings improved
- Recipes can be unlocked by leveling Survival skill on companions (except Winston)
- LUA Parsing through localization files
- Madness effect intensities lowered
- Theater Cultist dialogue lines improved
- Post-Combat mechanics for encounter during rest improved
- Inventory Capacity overload logic improved
- Improve combat dead character loot system
- Rework combat panic state ‘Locked Grip’
- Epilogue video ending has a new line

Change
- Combat character movement speeds are now faster
- Removed Spell Enhancement System
- The Colour Out Of Space combat dig icon
- Reinforced Hazard Suit skill requirement (Science 5)
- Witch House Attic now have resting point
- Attempt to cure Krogh no longer requires Bandages or Doctor’s Bag
- Remove flee cells from Outsider lynch combat
- Cycle of the Moon defect is now permanent
- Formula: Specimen Jar production quantity has been changed from 3 to 1.
- Richter now provides the player with 2 formaldehyde instead of 1 on non-medical approach.
- Combat Summary UI Angst Color is now red

Fix
Exploration
- A Possible Exit Quest rarely cannot be continued
- Dead Willows Wjatal combat flee exploit
- Settings sometimes reset to default when returning back to Landing Page
- Lost Man cutscene can trigger in Nithon even if you have him in your party
- Companions not following player
- Henchman recruitment bug
- French Hill Trap Door can be interactable randomly
- Blasted Street anomaly freezes player character
- Dead NPC loots can regenerate just like regular loots
- Struggle Begins infinite load
- Dead mobtsers can be infinitely looted exploit (Distillery)
- Settings cannot be saved properly
- Unlootable chest in the Post Office was breaking quest flow, leaving the player in limbo
- Inventory double click auto un-equipment of lantern if it is in lit mode
- Sanity damage carries over and even more decreases between saves
- Prevent combat trigger zone fire a combat when a cutscene is active (i.e headhunters)
- Corpse sprites not displaying correctly for dead companions in Exploration
- Artifact Brand of Taru defect does not appear on ANGST screen
- Artifact Venus of Willendorf defect does not appear on ANGST screen
- Consuming Disulfiral now clears all addictions
- Perks with item requirements not working properly
- Perks affecting critical failure not working properly
- Metabolism Catalyst and T.T.P. Mixture are now working properly
- State case where William can join party if not encountered at all
- Eduardo cannot trigger dialogue movement when entered riverside with a companion
- Angst gain increase takes into account all angst accumulated at current level
- Rare softlock case in exploration while trying to load combat
- Equipment modifiers also remove perk modifiers on unequip
- Wjatals activation state if entered combat via restricted zone
- Wilbur appears again in Nithon
- Blasted Street Fog does not kill player after loading game from combat
- Animation override issues
- Warehouse Sleeper cutscene can play twice

Combat
- Mind Control state getting stuck when character’s both main hand weapons are firearms are empty
- Mania getting stuck when character is unarmed
- Dead enemy loot issue after combat summary screen appears
- Old Blooded perk effect on panic state calculation
- Soft lock if travel combat encounter is re-started (Addresses most of the map related combat restarting bugs, seen as 'characters spawned on a different location in hub after combat and a soft lock is observed')
- Brand of Shame getting stuck on missed attacks
- Nameless Soldier’s Berserk state getting stuck when NS’ weapon has no ammo in it.
- Companion experiences sometimes not catching up with each other
- Made Man Distillery combat initiation
- Bleeding and similar states taken in combat did not clear properly after loading
- Reload a firearm during combat, in some cases caused lost of ammunition.
- The Sleeper Beneath combat getting stuck when more than 2 player party members move to the green hexes below The Sleeper Beneath.
- Two weapons appearing on character’s hands at the same time on combat.
- Dead henchmen can block progression
- Double reloading when accessing and initializing inventory from combat without first accessing from exploration, after a loaded game instance
- Updated Mi-Go display names on Nithon combats
- Combat panic state berserk issue causing a deadlock
- Additional AP checks for quick items on combat
- Combat panic state ‘Locked Grip’ state being stuck on character for the rest of combat
- Dead character prefabs on combat hubs
- Blood Circle logic rework
- Combat panic state henchmen drop weapon issue
- Hand of Nergal getting stuck on Outsider after the spells effect is cleared
- Outsider’s Spit of Al Razi blocking combat issue.
- Panic State dead character check
- Combat hex movement cost being more than 2 when more than 2 enemies die on the same cell Winston’s Tackle issue
- Party members still being in Stats pool even after they die
- Exp value for some of the Carrion Jack combat hubs
- Radial menu combat ability sub buttons filling method
- Combat freeze after restarting combat through Game Over UI
- HP / SP Bars In Combat Appear In Wrong Positions
- Panic state swap action issue
- Damage value calculation method on combat attacks
- Sanity zero characters being alive after combat ends issue
- Dropped items staying on the ground when attempted to be picked up on combat
- Critical Failure skill checks fixed
- Snapshot combat ability breaking attack flow
- Winston’s Tackle and Sonia’s Spectral Hands abilities being able to be cast to further enemies when another enemy is adjacent
- Radial menu not being able to open issue
- Companions not gaining xp when they escape/flee from combat and player character wins the combat afterwards.
- Quick item AP cost calculations
- Enemy still getting shattered even after the Petrified state is gone
- Players being able to attack fellow party members with Hands of Stone spell
- Outsider’s hands after Hands of Stone spell being cleared after spell wears off
- Random quick items being lost when another item is used on panic state and dropped due to panic
- Playable characters sometimes lose the ability to perform any actions after casting the "Children of Pazuzu" spell
- Die animation for Cultists and Cult Fedayeens where they play normal die animations instead of shatter while still being Petrified
- A breaking state that happens when another Blood Circle is cast before the previous one is still present
- Some spells not being able to be cast in a combat after fleeing a previous one
- Children of Pazuzu damage output inconsistencies

Changelog for Stygian Update 1.1.4 (19 December 2019) - Part II:

Fix (continued)
Crash
- Ward 10 pre-combat crash
- Keelan post-cutscene crash
- Setting VSync can cause crash

UI
- Tutorial UI Not Showing After Loading Game
- Rest anomaly for occult research, causing rest UI to soft lock
- In some cases inventory had items with empty technical names, causing UI to soft lock.Taken precautions against such cases
- Completing a combat encountered while at rest caused rest UI issues
- Weapon Powers and Maledictions cannot be revealed through Occult Research
- When companion cannot level up blocking entire tab menu
- Perks sometimes do not read stats correctly while leveling up
- Stacked levels showing higher level perks while leveling up
- Settings Resolution Pop-Up Can Stuck On Screen With Escape Key
- Combat Summary Pop-Up cannot close properly
- Hover tooltip display glitch when displaying nested rest activities and scrolling with mouse click instead of wheel
- Manuscripts show in rest screen if the spell is already learned
- Craft plans disappearing after learning new plan
- Buying multiple cigars if you do not have any cigar in your inventory counts as one cigar
- Trading for the first time with an NPC shows wrong cigar buy value
- Player can trade with Marino in Asylum during Cutscene
- Navigational Hub Switch UI issues
- Travel Map labels won’t disappear
- Resetting rest screen or closing rest screen does not clear activities properly
- Right-clicking rest activity clearing icon
- Research can continue after selling required items
- Canceling Rest window does not remove Research Plans
- Faithful perk can be acquired with all belief systems
- Rest UI to properly reset selected research activities when closed with ESC
- Combat Summary does not account for Angst increase effects
- Incorrect values of Total Angst and XP displayed with mouse hovering over corresponding bars in Character Sheet
- Pause and Quick load menus can be invoked with keyboard shortcuts while they should be unavailable
- Background and Archetype descriptions does not update after language switch
- Exploration menu settings button does not show in-game menu
- Exploration Menu "Options" hover text stays on screen after click
- Researching more blueprints than you can could break rest progression

Audio
- Tab Menu click sound does not read volume from SFX Volume
- Missing Warehouse Flesh Devourer Music

Cutscene
- Nameless Soldier end game cutscene codes not working accordingly to the narrative
- Party gets stuck when Richter returns back -Nithon Lost Man cutscene player while Lost Man is in party.
- Burning man cutscene (quest The Lost Patent) is auto triggered when main street loaded if player did not give him match
- Keelan combat cutscene not unregistering from cutscene events properly causing encounter combats to freeze if restarted

Dialogue
- Black Lips Return dialogue and companion interaction issues
- Theater Cultist gender addressing issues
- Chad initiates dialog in Travel Map after running away from Wjatal in Dead Willows
- Marino now properly wants his 40 cigs
- Chad / Bagakaw Repeatable Dialogue


Windows and Mac standalone installers updated: 1.0.4 ⇒ 1.1.1*.

* Note: GOG's changelog is labelled as 1.1.4, but there's a chance that it's just a copy/paste typo from the previous one (1.0.4), as the publisher themself has this update labelled as just 1.1 on Steam; otherwise there's a typo in the version number of the installers.


EDIT:
Linux standalone installer updated (1.0.4 ⇒ 1.1.1): 23 December 2019.

Update 1.1.5 (14 January 2020)


-Jeremy Parson soldier specific cutscene freeze has been solved.
-Equipping the Survivor's Backpack disables the possibility to unequip or switch backpacks for the entire party
-Fixed an issue on denizen AI
-Fixed an issue about progression escape cells
-Fixed coca vin marie and powdered cocaine not increasing AP issue in combat
-Improve reloading mechanics when more than one character equip same firearm
-Improve exploration stealth check mechanics to take stealth modifier into checks
-Fix Witch House Attic Transition Does Not Dissolve Rest Bed
-Fix CameraController Drag Depends On FPS
-Fix Blood Circle blocking panic state driven AI operations
-Fix Cutscene Triggering With Mouse Spamming
-Fix incorrect reloading of firearms when two characters equip same firearm
-Exploration stealth check mechanics changed to take stealth modifiers into account event the character's stealth stat is zero

Changelog for Stygian Update 1.1.6 (10 March 2020):

- Turkish Language Support
- Poison Spread Distillery Tank Investigation Fix
- Black Pyramid Entrance Cutscene Fix

Standalone installers updated (1.1.5 ⇒ 1.1.6): 11 March 2020.

Changelog for Stygian Update 1.1.7 (16 April 2020):

- Turkish localization overall typo and expression fixes
- Several fixes in Russian, German and French localization


Standalone installers updated (1.1.6 ⇒ 1.1.7): 17 April 2020.