Avoiding Circular Discrepancies for Col A = Col B (last row) and Col B = Col A (current row)?

Just add some judgment logic, hope to help you.

04_Ending Inventory_Display = 
VAR ItemID_AC = SELECTEDVALUE('Items'[Item ID])
VAR DATE_AC = LASTDATE('Calendar'[Dates])
VAR T0 =
    FILTER (
        ADDCOLUMNS (
            CROSSJOIN ( ALL(  'Calendar'[Dates] ), ALL( 'Items'[Item ID] ) ),
            "@IN",[02_Receipts_Display],
            "@OUT",[03_Forecast],
            "@END0", [04_Ending Inventory]
        ),
        NOT ( ISBLANK ( [@END0] ) )
    )
VAR T1 =
    ADDCOLUMNS (
        T0,
        "@Index",
            COUNTROWS (
                WINDOW (
                    1,
                    ABS,
                    0,
                    REL,
                    T0,
                    ORDERBY ( 'Calendar'[Dates], ASC, Items[Item ID], ASC ),
                    PARTITIONBY ( Items[Item ID] )
                )
            )
    )
VAR T2 =
    ADDCOLUMNS (
        T1,
        "@Acc",
            VAR R = [@Index]
            VAR ItemID = [Item ID]
            VAR T = FILTER ( T1, [Item ID] = ItemID  && [@Index] <= R )
            VAR Acc = SUMX ( T, [@END0] )
            RETURN
                Acc
    )
VAR T3 =
    ADDCOLUMNS (
        T2,
        "@isAdd",
            VAR R = [@Index]
            VAR ItemID = [Item ID]
            VAR T = FILTER ( T2,   [Item ID] = ItemID && [@Index] <= R )
            RETURN
                MINX ( T, [@Acc] )
    )
VAR T4 =
    ADDCOLUMNS (
        T3,
        "@minIndex",
            VAR R = [@Index]
            VAR ItemID = [Item ID]
            VAR T = FILTER ( T3, [Item ID] = ItemID && [@Index] <= R )
            VAR MIN0 = MINX ( T, [@Acc] )
            VAR TT = FILTER ( T, [@isAdd] = MIN0 )
            VAR I = MINX ( TT, [@Index] )
            RETURN
                I,
        "@Diff",
            VAR R = [@Index]
            VAR ItemID = [Item ID]
            VAR T = FILTER ( T3, [Item ID] = ItemID && [@Index] <= R )
            VAR MIN0 = MINX ( T, [@Acc] )
            VAR TT = FILTER ( T, [@isAdd] = MIN0 )
            VAR I = MINX ( TT, [@Index] )
            VAR DIFF = SUMX ( FILTER ( T, [@Index] = I ), [@END0] )
            RETURN
                DIFF
    )
VAR T5 =
    ADDCOLUMNS (
        T4,
        "@END1",
            VAR R = [@Index] - 1
            VAR ItemID = [Item ID] 
            VAR T = FILTER ( T4, [Item ID] = ItemID && [@Index] = R )
            VAR END0_Previous = SUMX ( T, [@END0] ) 
            VAR X =
                SWITCH (
                    TRUE (),
                    [@END0] < 0 && [@IN] - [@OUT] > 0, [@IN] - [@OUT],
                    R >= [@minIndex] && [@Diff] < 0, [@END0] - [@Diff],
                    R < [@minIndex] && [@Diff] < 0, 0,
                    END0_Previous < 0, [@END0] - END0_Previous,
                    [@END0]
                )
            RETURN
                X
    )
VAR T6 =
    ADDCOLUMNS (
        T5,
        "@BEGIN1",
            VAR R = [@Index] - 1
            VAR ItemID = [Item ID] 
            VAR T = FILTER ( T5, [Item ID] = ItemID && [@Index] = R )
            VAR END1_Previous = SUMX ( T, [@END1] )
            VAR BEGIN1 = IF ( END1_Previous < 0 || END1_Previous = BLANK(), 0, END1_Previous )
            RETURN
                BEGIN1
    )
VAR T7 =
    ADDCOLUMNS (
        T6,
        "@END2",
        SWITCH (
            TRUE (),
            [@BEGIN1] + [@IN] - [@OUT] > 0, [@BEGIN1] + [@IN] - [@OUT],
            [@END0]<0 && [@BEGIN1] + [@IN] - [@OUT] <= 0, 0,
            [@END0]
        )

    )
VAR T8 = FILTER ( T7, [Dates] = DATE_AC && [Item ID] = ItemID_AC )
VAR RESULT = SUMX ( T8, [@END2] )
RETURN
    RESULT

01_Beginning Inventory_Display = 
VAR DATE_START0 =
    CALCULATE ( FIRSTDATE ( 'Calendar'[dates] ), ALL ( 'Calendar' ) )
VAR DATE_END0 =
    LASTDATE ( 'Calendar'[dates] )
VAR TF0 =
    HASONEVALUE ( 'Calendar'[dates] ) //日
VAR TF1 =
    HASONEVALUE ( 'Calendar'[YearWeek] ) //周
VAR TF2 =
    HASONEVALUE ( 'Calendar'[YearMonth] ) //月
VAR TF3 =
    HASONEVALUE ( 'Calendar'[YearQuarter] ) //季度
VAR TF4 =
    HASONEVALUE ( 'Calendar'[YearHalf] ) //半年度
VAR TF5 =
    HASONEVALUE ( 'Calendar'[FY00] ) //年度
VAR N0 =
    SWITCH (
        TRUE (),
        TF0, 0,
        TF1,
            DATEDIFF (
                FIRSTDATE ( 'Calendar'[StartOfWeek] ),
                LASTDATE ( 'Calendar'[EndOfWeek] ),
                DAY
            ),
        TF2,
            DATEDIFF (
                FIRSTDATE ( 'Calendar'[StartOfMonth] ),
                LASTDATE ( 'Calendar'[EndOfMonth] ),
                DAY
            ),
        TF3,
            DATEDIFF (
                FIRSTDATE ( 'Calendar'[StartOfQuarter] ),
                LASTDATE ( 'Calendar'[EndOfQuarter] ),
                DAY
            ),
        TF4,
            DATEDIFF (
                FIRSTDATE ( 'Calendar'[StartOfHalfYear] ),
                LASTDATE ( 'Calendar'[EndOfHalfYear] ),
                DAY
            ),
        TF5,
            DATEDIFF (
                FIRSTDATE ( 'Calendar'[StartOfYear] ),
                LASTDATE ( 'Calendar'[EndOfYear] ),
                DAY
            ),
        0
    ) + 1
VAR DATE_END1 =
    SWITCH (
        TRUE (),
        TF0, DATEADD ( DATE_END0, - N0, DAY ),
        TF1, DATEADD ( LASTDATE ( 'Calendar'[EndOfWeek] ), - N0, DAY ),
        TF2, DATEADD ( LASTDATE ( 'Calendar'[EndOfMonth] ), - N0, DAY ),
        TF3, DATEADD ( LASTDATE ( 'Calendar'[EndOfQuarter] ), - N0, DAY ),
        TF4, DATEADD ( LASTDATE ( 'Calendar'[EndOfHalfYear] ), - N0, DAY ),
        TF5, DATEADD ( LASTDATE ( 'Calendar'[EndOfYear] ), - N0, DAY ),
        DATE_START0 //无筛选的时，默认日期表期初。
    )
VAR DATE_END2 =
    IF ( ISBLANK ( DATE_END1 ), DATE_START0, DATE_END1 ) //兼容 dateadd 后的空值，注意日期表的两个端点。
VAR DATE_TABLE0 =
    DATESBETWEEN ( 'Calendar'[dates], DATE_START0, DATE_END2 )
VAR _Begin =
    CALCULATE ( [04_Ending Inventory_Display], DATE_TABLE0 )
VAR IN0 =
    CALCULATE ( [02_Receipts], DATE_TABLE0 )
VAR OUT0 =
    CALCULATE ( [03_Forecast], DATE_TABLE0 )
RETURN
    IF ( [03_Forecast], COALESCE( _Begin,IN0-OUT0), BLANK () )