Strange update of a linked cell

I have 3 Excel files File1.xls, File2.xlsm, File3.xlsm.

Every day File1.xls is produced and saved through a process. File2.xlsm is let's say the today file and
File3.xlsm is the same as File2.xlsm, just saved 6 months ago.

File2.xlsm and File3.xlsm in one worksheet have the following formula:

=SUMPRODUCT('Path1\[File1.xls]Wsh1'!$S$2:$S$1000,--('Path1\[File1.xls]Wsh1'!$A$2:$A$1000=A45))/1000000

The saved value of today's File2.xlsm on the cell with the above formula is 334 and the saved value on the same cell to the old File3.xlsm is 324.

I open File2.xlsm, it asks me to update or not the external links and I say No. The cell has 334.

I open concurrently File3.xlsm (the old version of the file), it asks me to update or not the external links and I say No. The cell has 324.

I check File2.xlsm and the value has changed from 334 to 324, just because I opened File3.xlsm.

Why do I have this strange update? I told it to not update the links. Additionally, it doesn't update with the today's File1.xls but with the saved number of the old file.

Thank you.