My experience so far. Hope this gives some valuable info.

- V4.01 was stable with no crashes and no problems loading saves. BUT with bugs mentioned below, PLUS broken deal history.
- V4.12 Deal history seems fixed. Crashed occasionally when moving a unit or capturing a city. Save games can become unloadable.

For the latest experiment I made a completely fresh install of the game:
> Almost brand new legit Windows 11 installation. Deleted the game. Deleted the folder in 'my games'. Deleted anything that remained in the main install folder. Reinstalled game.
> Launched a game without mods. No problem. Exit.
> Went to mods. Subscribed to gaia core v4.12. Launched a game on some random map. No obvious problem so far. Back to main menu.
> Subscribed to the remaining gaia mods. Tried to launch 'isolation' map. Automatically defeated on start. Exit to main menu... crash. Start the game... loading...crash.
> Deleted everything in cache folder -> Launch game -> Mods -> Big continents advanced setup... seems ok but with some bugs

**Bugs:**
These bugs are applicable to v4.12.
>>> Victory Conditions: Disabled all victory conditions apart from Time and Domination, but in the victory progress interface Economic and Religion victory are still being tracked. Other victories are correctly marked as disabled.
>>> Espionage: Hovering over your spy shows TXT_EO...blabla. Spy makes 0 progress in any city. The bar never fills up and spy power = 0. Only fills up for coups in city states.
>>> Can build an unlimited number of Railroad artillery even though the limit is supposed to be 2. I have built 6 so far. Same with snipers but I think I hit a limit but it was definitely more than 1 (not 100% sure as my save game is dead). Barbarians spawn multiple railroad artillery... and keep spawning the sniper which is annoying AF.
>>> Don't know if this was intended but railroad artillery can go outside a railroad. It's comical to see barbarian railroad artillery crawling through forests and hills.
>>> Rocket launcher animation is waaaay too slow and no rockets are visible. Platform just goes up and down.
>>> The game ALWAYS crashes when going back to main menu. You need to delete the cache each time you want to launch the game.
>>> Loading save games crashes more often than not, even though no changes were made to mods. When it does crash, it always crashes and the save game is dead.
>>>> Lua log has no runtime error after this crash but says "[124264.812] CanalPlacement: Improvement destroyed" multiple times. Not sure if its relevant.
>>>> Clearing mod user data folder or cache does not help.

**Other:**
>>> Need to remove the indirect fire promotion in my opinion because it's stupidly unrealistic (muskets firing over mountains wut :D). The +1 range one is also stupidly unbalanced.
>>> Need to remove breacher and other AOE promotions because its insanely unbalanced and unrealistic. It also affects land units when you kill a sea unit with a sea unit, which is hilarious.
>>> I know this is made for balance for 1UPT, but it is comical how muskets can fire 2 tiles away at helpless riflemen :D If multiple upt would be the default then maximum range for such units should definitely be 1.

Note:
I always used 3 other mods besides the gaia ones:
- SOD this Mod
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1285970979
- Barbarians evolved (with the most minimal settings just to get barb healing and different era names)
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=485249197
- Tribal Village
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2837004565

One more small thing forgot to mention:
- There is a duplicate button to repair a pillaged tile for some reason.

Thanks for the detailed report. Would you mind sending me a friends request as I have a few questions and my friend list is capped (so I'm not even sure it will work but worth a try).

Accepted your request

I would like to piggyback off the above (the name is censored, funnily enough, very cool Steam) bug report, actually, I found the same findings to be true for myself. I will add a few additional observations. I hope they are helpful; I apologize if not, I do not wish to waste your time needlessly.

All of these tests occurred over the last 3 weeks or so. I have updated mods whenever new versions were available, always clearing cache and userdata and starting a fresh game after updates. Mods used were: Core Mod, Sapiens, the Civ pack, the IGE, Places of Worship, Suzerainty, Returning Fog, and Core Mod UI. At this point my computer is several years old, but it is still a very powerful one, I do not think realistically hardware limitations are an issue. Windows 11.

- The later the game goes, the higher a chance seems to be that it crashes on loading. I have rarely crashed when loading the first 100 turns or so (on Marathon speed,) and pretty frequently afterwards. When a save game crashes on loading from a fresh start of the program, the save file is then unusable; nothing I do can help it load again, not clearing the cache, nor doing a full reinstall of the mods or Civ itself. For this reason, I have not managed to get a game past the Industrial era.
- Loading a game without having to clear cache/moduserdata has only worked on turn 1 saves. I have never been able to load a game past turn 1 without the game crashing and having to restart with clearing data.
- Occasionally mouseover tooltips 'lag' and show the tooltip for the previous thing I moused over, or get stuck on a random tooltip I had seen before. Especially noticeable when mousing over luxuries for monopoly information. This is not incredibly frequent nor fatal.
- The new sea resources, Kelp and minerals, never have sprites, though they seem to affect tile yields as normal.
- Bismarck's unique barbarian conversion ability has never worked for me. Admittedly, I have not tried him in the last couple of versions, so that's only a tentative report.
- The IGE in particular seems to be the cause of a lot of my crashes. I use it a lot for observing AI activity and it seems as though switching to another AI's perspective is very risky. Generally switching to an AI with more than 2 cities immediately causes a crash to desktop; as of two weeks ago (I don't remember the exact Core mod version it was, I think 412) these crashes are also inevitably impossible to then recover from, and any attempt to load any saved game causes a CTD on loading.
- Strangely, a lot of these issues were not present around a month ago. This was back when Coconuts were still a resource, if that gives any indication of the version; I apologize dreadfully for the vague time, I only started keeping detailed notes a few days ago. Although I still had rare crashing issues on seemingly random moments of the game processing something, I was able to load games without problems.

I would like to add to my previous comment; When just launching a game with Core Mod, I can successfully exit to main menu on turn 1. Doing so with the other mods I mentioned active crashes the game. At some point I intend to do a test to see which one causes the issue, but if it is a mixture of mods, well... I hope it's not as that'll be much harder to test for.

So it would appear as though so far, attempting to exit to menu with ANY combination of mods active crashes the game, but one mod at a time is fine. I'm not actually sure why this would be the case and it's illogical enough that I'm willing to suspect some kind of ingrained issue on my part, though I've tried every cleanse and reinstall known to man at this point, or at least known to me, which is a much narrower spectrum but still decent.

Other small issues that I've noticed; any event that gives negative gold to buildings shows up as a '+-num' in tooltips. Hardly critical and mostly amusing.
- The Akapana wonder does not seem to work; I cannot acquire Challa Rituals whether I found the religion, or capture it. Unfortunately the AI also seems to prioritize Akapana very, very highly and has consistently taken it as the worship building first in all games. From what I can see they do not have the ability to boost it either.
- I don't know whether it's intended or not, but the AI seems to favor spamming scouts for the first ~100 turns of gameplay or so. I counted 9 scouts for Sweden in the first 100 turns, at the expense of having almost no other military. (The game speed is Marathon, I don't know if that matters.)
- Occasionally city states will give the random mission to stage a coup in another city state, but they can do so for city states with no suzerain. If this happens (and it seems to happen pretty often,) they cancel the mission on the next turn.
- Again something I don't know whether it's intended or not, but there seems to be an inordinate amount of religions on Huge maps. 10 religions were founded in my current game; given that the default number of civilizations is 12, that seems quite high. If it is intended, would it be possible to lower it manually?