It likely has to do with the wage index going down last year. -1.54%. Run the numbers, and compare to last year using the -1.54.
COLA amounts for those already drawing SS, aren't reduced if CPI goes down. Those under 62, not drawing, have their estimate based on AWI, which can be reduced from year to year, if the AWI goes down. This will be especially apparent if you have stopped working prior to 62, and have years of zero earnings. If that is the case, AWI is the only variable that controls your future benefit amount. It usually goes up, but not last year.