Creating a new column, and setting it = an old column, is causing a Circular Dependency Error. Why?

I was trying to help a colleague (clearly I am not qualified to). They're getting a circular dependency error.

In testing, I notice, that say - they have Column A in Table_1.

I fI create Column B, with simply the formula Column B = Table_1[column A]. This causes Column B to give a circular dependency error.

Now, Column A is a ridiculous column, but I don't understand how simply referencing it, in a brand new column, is triggering a circular dependency error?

That 'Column A' for reference (which I'll clean up with SWITCH for them anyway)

Matrix_Acct_Type = 
VAR MATRIXACCTTYPE =
IF (
    LOOKUPVALUE ( Customer[CustNBR], Customer[CustNBR], SFDC_Opportunity[CustNBR] )
        = BLANK (),
    (
        IF (
            SFDC_Opportunity[Product] = "AP Assist",
            "Auto",
            IF (
                SFDC_Opportunity[Sales Team] = "Automotive",
                "Auto",
                IF (
                    CONTAINSSTRING ( SFDC_Opportunity[Channel Partner], "CDK" ),
                    "Auto",
                    IF (
                        SFDC_Opportunity[OwnerId] = "005A0000005JRpZIAW",
                        "Auto",
                        IF (
                            ISBLANK (
                                LOOKUPVALUE (
                                    SFDC_Account[Sub Industry],
                                    SFDC_Account[AccountId], SFDC_Opportunity[AccountId]
                                )
                            ),
                            "Standard",
                            IF (
                                CONTAINSSTRING (
                                    LOOKUPVALUE (
                                        SFDC_Account[Sub Industry],
                                        SFDC_Account[AccountId], SFDC_Opportunity[AccountId]
                                    ),
                                    "Automotive"
                                ),
                                "Auto",
                                "Standard"
                            )
                        )
                    )
                )
            )
        )
    ),
    IF (
        LOOKUPVALUE (
            Customer[CustProductType],
            Customer[CustNBR], SFDC_Opportunity[CustNBR]
        ) = "AP Assist",
        "Auto",
        IF (
            LOOKUPVALUE ( Customer[SFOwner], Customer[CustNBR], SFDC_Opportunity[CustNBR] ) = "Pam Cichoke",
            "Auto",
            IF (
                CONTAINSSTRING (
                    LOOKUPVALUE (
                        Customer[ChannelPartner],
                        Customer[CustNBR], SFDC_Opportunity[CustNBR]
                    ),
                    "CDK"
                ),
                "Auto",
                IF (
                    CONTAINSSTRING (
                        LOOKUPVALUE (
                            Customer[OrgSubIndustry],
                            Customer[CustNBR], SFDC_Opportunity[CustNBR]
                        ),
                        "Automotive"
                    ),
                    "Auto",
                    "Standard"
                )
            )
        )
    )
)
RETURN MATRIXACCTTYPE