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My testing was able to produce a SUMIF problem that appears to match yours. I don't know what causes it or how consistent it is. It appears that SUMIF did not recognize a match when the value being tested against the criteria is not in the first column of the range. The value "Best Seller" in F:H that should match U1284 is in G or H but not in F. This results in a sum of 0 and your accounting format causes that to display as a dash.
The following workaround appears to produce the desired result:
=SUM(IF((--($F$6:$F$1537=U1280))+(--($G$6:$G$1537=U1280))+(--($H$6:$H$1537=U1280)),$E$6:$E$1537,0))
This goes in W1280 and gets copied down till the last key word in column U.
If you put it in column X instead, you may discover some of the values in W are incorrect but don't catch the eye the way the dash did.