It seems the line has been lowered from KC -3 1/2. to KC -3 at pretty much all the Las Vegas casinos, and according to the Las Vegas Review Journal the books may lose some big-bucks if Kansas City wins, but doesn't cover the spread.
"The worst-case scenario for BetMGM would be if the Chiefs won by three. If that happens, the book would pay out all Bucs bets at +3½ and refund all bets at 3.
The best-case scenario at most books, including William Hill, Station and the Westgate, would be for Kansas City to win but not cover."