Wrong expression result

Hi All,
the expression:
if([Last week row].[Week Salary Count]=1,[Date Start]+7,[Last Week row].[Date Start])

result is wrong
image

but in expression test builder it returns correct.

assist, please.

thanks

I’d guess [Date Start] is a blank value when the expression is evaluated in the form.

strange, when form runs the g sheet is already with [date start]. so the initial value should refer to that.
as the expression aimed at, it supposed to collect the most recent [date start] and add 7 if the condition is met.
image

it only behaved this way when [Week Salary Count] = 1, if its other than one then it is ok.

If [Week Salary Count] is 1, is there a [Last week row]?

[Last week row] is a VC.
If [Week Salary Count] is 1 it is supposed to give the new [date start]