It is not just for addition or AUTOSUM formulas that are not updating automatically.
Step 1: Open the workbook with the formula that is not updating.
Note that this setting applies to every formula in your workbook.
This means any cell which contains any type of formula.
The cell references were all correct, but for whatever reason they would not update.
Even more mysterious, the calculations worked fine on some machines, but not others. That can happen if the first workbook that you open in an Excel session was saved as Manual calculation.
It seems that when the data in his worksheet changes, the SUMIF function doesn't automatically update.
He is, however, able to update the formula if he selects it, presses F2 (to jump into edit mode) and then press Enter.
The only way the to update the cell is to click on the formula and hit Enter or Tab.
I tested the issue out on a couple of new speedsheets (both saved on the same shared drive) and it's still happening.
When updating an Excel spreadsheet formulas do not update automatically as values are entered or updates.