In the past, fields were added to tabs directly through the field settings in Database > Fields. For Partners looking to migrate to adding custom fields to custom tabs using the Form Builder instead of using field settings, take precautions to ensure that the source key of exports and filters being used in existing queries continues to function as intended.
When migrating from creating tabs with the field settings to building them with Form Builder, before removing the tab in the Tab setting, name the Category for the field with the exact same name as the tab.
Once the Category is renamed appropriately, the Tab selection may be removed. The field can then be saved with the Category set to the name that the tab once was.
NOTE: If a Category already exists in the field settings, do not take this action.