The problem: all of a sudden you cant edit all or some of your fields using sharepoint designer / columns have become greyed out in the settings.
eg:

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note some of the columns are greyed out, cant be modifed here or used in the workflow (you can read the fields but not set them)

The solution: re publish your form and go into every greyed out item, click modify, then click “allow users to edit data in this field by using datasheet or properties page” then republish

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