Making autopostback the control values are lost

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C#

.NET

Hello
I am developing a website in vs2015. In a form I have several dropdownlist that selecting a value on them change other values in the form.
the problem is that this works well when the user is logged in, but when it is not, by making autopostback the control values are lost.
Any idea why this happens?
Thank you

What I have tried:

the code that I use is only in the load and runs once because I have put conditional

if (!IsPostBack)
            {
}

and dropdownlist controls are filled by ObjectDataSource