• Create a 'JsonError' mod in WB
• Create a file <moddir>\JsonError\scripts\Game\GameCore\Modded\SDRC_BaseGameMode.c
• Copy the code in Additional Information
• In WB, Create a world with GameMode_Plain:
• Compile and start the game.
• A simple file JsonError.json is created under profile\JsonError\
• File content will be: "{"value":1,"name":"dummy","vecval":[1.0,2.0,3.0]}"
• Rerun the code and the file values are loaded properly
• Change the file content to: "{"value":1,"name":"dummy","vecval":[2.0,3.0,4.0]}"
• Rerun the code and the file values are loaded properly
• Change the file content to: "{"value":1,"name":"dummy","vecval":[2.0,3,4.0]}". NOTE: 3.0 is changed to 3
• The file is proper json in case it's tested with a validator.
• Rerun the code and the file fails to load. The default values are used.

IMO, the vector value should be loaded even if it would be just [1,2,3]. With other float variables this works properly.

modded class SCR_BaseGameMode
{
private ref SDRC_ConfJsonApi m_ConfJsonApi = new SDRC_ConfJsonApi();

//------------------------------------------------------------------------------------------------

    override void OnGameStart()
    {
        super.OnGameStart();
		m_ConfJsonApi.Load();
		Print(m_ConfJsonApi.conf.vecval);
    }

};

class SDRC_Conf
{
int value = 1;
string name = "dummy";
vector vecval = "1 2 3";
}

//------------------------------------------------------------------------------------------------
class SDRC_ConfJsonApi : SDRC_JsonApi
{
const string DC_CONF_FILE = "JsonError.json";
ref SDRC_Conf conf = new SDRC_Conf();

//------------------------------------------------------------------------------------------------
void Load()
{

		SCR_JsonLoadContext loadContext = LoadConfig(DC_CONF_FILE);
		
		if (!loadContext)
		{
			SetDefaults();
			Save("");
			return;
		}

		loadContext.ReadValue("", conf);

}

//------------------------------------------------------------------------------------------------
void Save(string data)
{

		SCR_JsonSaveContext saveContext = SaveConfigOpen(DC_CONF_FILE);
		saveContext.WriteValue("", conf);
		SaveConfigClose(saveContext);

}

//------------------------------------------------------------------------------------------------
void SetDefaults()
{

}
}

//Helpers/SDRC_JsonApi.c

For readable jsons, use https://jsonformatter.org
NOTE: View .json in Notepad++ - press Ctrl+Alt+Shift+J
// NOTE: Format .json in Notepad++ - press Ctrl+Alt+Shift+M

//------------------------------------------------------------------------------------------------
class SDRC_JsonApi : JsonApiStruct
{
private string m_FileName = "";

//------------------------------------------------------------------------------------------------
SCR_JsonLoadContext LoadConfig(string fileName)
{

		SetFileName(fileName);
		SCR_JsonLoadContext loadContext = new SCR_JsonLoadContext();
		
		bool success = loadContext.LoadFromFile(m_FileName);
		
		if (!success)
		{
			return null;
		}
		
		return loadContext;

}

//------------------------------------------------------------------------------------------------
SCR_JsonSaveContext SaveConfigOpen(string fileName)
{

		SetFileName(fileName);
		
		SCR_JsonSaveContext saveContext = new SCR_JsonSaveContext();
		
		return saveContext;

}

//------------------------------------------------------------------------------------------------
void SaveConfigClose(SCR_JsonSaveContext saveContext)
{

		string dataString = saveContext.ExportToString();
		ExpandFromRAW(dataString);
		
		if (!saveContext.SaveToFile(m_FileName))
		{
			Print("[SDRC_JsonApi] Config save failed to: " + m_FileName, LogLevel.ERROR);
		}
		else
		{
			Print("[SDRC_JsonApi] Config saved to: " + m_FileName, LogLevel.DEBUG);			
		}

}

//------------------------------------------------------------------------------------------------
override void OnError(int errorCode)
{

		// errorCode is EJsonApiError
		// Event called when pending store operation is finished - callback when error happened
		Print("[SDRC_JsonApi] Error loading config. " + SCR_Enum.GetEnumName(EJsonApiError, errorCode), LogLevel.ERROR);

}

//------------------------------------------------------------------------------------------------
void SetFileName(string fileName)
{

		string path = "";
		string directory = "JsonError";
		
		path = "$profile:/" + directory + "/";

		if (!FileIO.MakeDirectory(path))
		{
			Print("[SDRC_JsonApi] Could not create path: " + path, LogLevel.ERROR);
		}
				
		m_FileName = path + fileName;

}
}