Operators AND - OR in Nested IF

I am struggling with a silly formula but I am not able to find the proper solution. I know it should be easy .....

CS_Universe = 
IF (
    ZV[OrgCom] = "CUSTORG"&& ZV[IDCust] = "491"&& ( ZV[IDDel] = "SPD99"
        || ZV[IDDel] = "WAR99"
        || ZV[IDDel] = "DPD99"
        || ZV[IDDel] = "FOC99"
        || ZV[IDDel] = "KBD99" );
    "1CS";
    IF (
        ZV[OrgCom] = "CUSTORG"&& ZV[IDCust] = "491"&& (ZV[CounFinGood] = "MX"   
            || ZV[CounFinGood] = "RU"
            || ZV[CounFinGood] = "AR"
            || ZV[CounFinGood] = "CN")
            ;
        "2CS";
        IF (
            [OrgCom] = "CUSTORG"&& [IDCust] <> "491"&& [ECC] = "X"&& ( ZV[IDDel] = "SPD99"
                || ZV[IDDel] = "WAR99"
                || ZV[IDDel] = "DPD99"
                || ZV[IDDel] = "FOC9"
                || ZV[IDDel] = "KBD99" );
            "3CS";
            IF (
                [OrgCom] = "CUSTORG"&& [IDCust] <> "491"&& [ECC] = BLANK ()&& ( ZV[IDDel] = "SPD99"
                    || ZV[IDDel] = "WAR99"
                    || ZV[IDDel] = "DPD99"
                    || ZV[IDDel] = "FOC99"
                    || ZV[IDDel] = "KBD99" );
                "4CS";
                BLANK ()
            )
        )
    )
)

This formula work perfectly except the 2nd if that should write "2CS".  I also moved it bottom just to test.

Then I added a new calculated column putting only the following and I have got the right result.

IF (
        ZV[OrgCom] = "CUSTORG"&& ZV[IDCust] = "491"&& (ZV[CounFinGood] = "MX"   
            || ZV[CounFinGood] = "RU"
            || ZV[CounFinGood] = "AR"
            || ZV[CounFinGood] = "CN")
            ;
        "2CS";

So syntax is correct and the order of operators too, otherwise the first IF above should not work.

Please is there someone who could explain me how to fix it?

Thanks