I find this rather confusing:

Cell M7
=IF(SUM(H7:L7)=0,"",SUM(H7:L7))

Cell M8
=IF(COUNTIF(H8:L8,"W")<1,"",COUNTIF(H8:L8,"W"))

Cell M9
=IF(SUM(H9:L9)=0,"",SUM(H9:L9))

When I enter the formula in M7 and M8 everything works as expected,
however when I enter the formula in M9 I get the diamond with the
exclamation indicating "Inconsistent Formula" to the left of Cell M8.
Can anyone explain why?
Thanks