Lookup Fields are not available for mapping in the Data Import Wizard

If Users report that fields are no longer available for mapping in the Data Import Wizard, ensure that the affected user has access to the missing fields. 

1. Field Access: Confirm the affected user has access to the missing fields.
   
   

2. Profile and Record Type: Ensure the user's profile has at least one assigned record type, and the corresponding page layout includes the missing fields.
   
   

3. Field-Level Security: If the fields are on the page layout, double-check the user's profile's field-level security settings. Verify they have access to the field. You can review field access by field, profile, or record type in Setup by searching for "Field Accessibility."
   
   

4. Regarding custom Master-Detail and Lookup relationships: They're fundamentally similar, except Master-Detail fields are always required, while Lookups are optional. The screenshot below shows a custom object import with a custom lookup field. During import, Standard lookups can be matched using either the Salesforce record ID or the record name. We need to ensure this same flexibility (matching by ID or name) is available for our custom lookup fields as well.