I have 3 tables:

RawScore
: a table of raw scores for players each day 
ScoreMod
: a table of modifiers to each players’ daily raw score 
Total
: a table that calculates their total effective scores
I use the following function to calculate each player’s daily effective score (raw scores + modifiers):
=LET(
MyDate, FILTER(RawScore[Date],RawScore[Name]=Total[@Name]),
MyRawScore,FILTER(RawScore[Score],RawScore[Name]=Total[@Name]),
MyModifier,XLOOKUP(
MyDate,
FILTER(ScoreMod[Date], ScoreMod[Name]=Total[@Name],0),
FILTER(ScoreMod[Modifier], ScoreMod[Name]=Total[@Name],0), 0),
MyModifier + MyRawScore)
When I use =SUM(EffectiveScore)
for Tom’s total score in the Total table, the result is incorrect, becoming 300. However, when I use =SUM(+EffectiveScore)
for Tom’s total score, the result is the correct total score, 280.
My question is, why the formula without the +
can not get me the correct answer, and why adding a +
gets me the right answer?
Link to the document: https://1drv.ms/x/s!At1ltp8PtMKgpsP2cOPZStP89ozpw