Rows are numbered starting at 1 in the actual smartsheet view, and when it exports to Excel row number 1 is now the header, which causes the predecessor references to be wrong.
I wonder if the fix to this would be to have an actual Row ID column in smartsheet in addition to the row reference? Another option is to prompt in the export menu with a disclaimer that it might not allow for re-import if you shift things.
I attached 2 screenshots showing both the Smartsheet file, and the Excel exported file. The template I used for this sheet is "Project"

