How to improve performance issues for DAX Formula

I agree with the suggestion to use the ADDCOLUMNS pattern. Here are two other ways to write your expression (I think), but the [01. Order Units] measure may be the reason for slowness. What is the expression for that measure?

_X̄Production LT =
VAR summary =
    CALCULATETABLE (
        ADDCOLUMNS (
            SUMMARIZE (
                'PO Daybook',
                'PO Daybook'[__.01. Production LT],
                'PO Daybook'[PO Number]
            ),
            "cOrdUnits", [01. Ordered Units]
        ),
        KEEPFILTERS ( 'Product'[Newness Classification] <> "Collab" ),
        KEEPFILTERS ( ISBLANK ( 'PO Daybook'[Customer Reference Number] ) ),
        'PO Daybook'[__01. Production LT] > 49,
        NOT ( ISBLANK ( 'PO Daybook'[12. Available Ship Date] ) )
    )
VAR num =
    SUMX ( summary, [cOrdUnits] )
VAR denom =
    SUMX ( summary, [cOrdUnits] * 'PO Daybook'[__01. Product LT] )
RETURN
    DIVIDE ( num, denom )

Option 2

_X̄Production LT =
CALCULATE (
    DIVIDE (
        SUMX ( DISTINCT ( 'PO Daybook'[__01. Production LT] ), [01. Ordered Units] ),
        SUMX (
            DISTINCT ( 'PO Daybook'[PO Number] ),
            [01. Ordered Units] * 'PO Daybook'[__01. Product LT]
        )
    ),
    KEEPFILTERS ( 'Product'[Newness Classification] <> "Collab" ),
    KEEPFILTERS ( ISBLANK ( 'PO Daybook'[Customer Reference Number] ) ),
    'PO Daybook'[__01. Production LT] > 49,
    NOT ( ISBLANK ( 'PO Daybook'[12. Available Ship Date] ) )
)