MoM % Variance

Looking at your data, Snapshot Month is already stored as the first day of each month. You can use EDATE to get the previous month directly.

MoM % Variance =

VAR CurBal =

    SUM('Exposure Balance Monthly'[Exposure Balance])

VAR CurMonth =

    MAX('Exposure Balance Monthly'[Snapshot Month])

VAR PrevMonth =

    EDATE(CurMonth, -1)

VAR PrevBal =

    CALCULATE(

        SUM('Exposure Balance Monthly'[Exposure Balance]),

        REMOVEFILTERS('Exposure Balance Monthly'[Snapshot Month]),

        'Exposure Balance Monthly'[Snapshot Month] = PrevMonth

    )

RETURN

    DIVIDE(CurBal - PrevBal, PrevBal)

This compares each month's balance with the previous month's balance and returns the percentage increase or decrease.

Make sure `Snapshot Month` has the Date data type, not Text.