When editing, the sign up date field changes to the current date

Got it. That did it. One last thing I noticed on the edit form. When editing, the sign up date field changes to the current date

The date changes, because it is set to obtain the current date:

You could duplicate that field(click on it's gear icon>>Duplicate) and set the Default Date to None for this new duplicated field. Then create a condition to pass the value from the original date field to the duplicated one:

 

 

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