IF FUNCTION Problem, returning false when number is less than 1000

Hi everybody

Usually I'm able to find the solutions to my Excel problems online, but this one is perhaps too specific.

Here's in the formula:
=IF(SUM(AC17,AA17,Y17,W17,U17,S17,Q17,O17,M17,K17,I17,G17)=(AF19-AF24),(AF19-AF24),"false")

So I'm using the formula above to check that the sum of a range of cells equals AF19-AF24.
If true, then it should return the AF19-AF24 total. If false, it should return error.

This spreadsheet is not new, I've been using this formula for some time, but only now I've realised that if the AF19-AF24 result is less than 1000, I get a "false", even if the numbers are equal to the SUM range.

Also, it doesn't matter which cell/column/row I change in the spreadsheet, if the result leads to more than 1000, I get the number I should get from the IF function, but if the result is less than 1000, it gives me a "false", when I should only get a false if the numbers don't match.

Not sure if I was very clear, please let me know if you can help.

EDIT/ADDITIONAL INFORMATION

I've just noticed that I get "false" if the result from the formulas is between -999 and 999.

I'm attaching here a sample spreadsheet, and the cell with the issue is in yellow.

Thank you all for your interest in helping!