When I was processing return this past Saturday, I was asked for last name and S.S. No. for W-2, the information from which had been exported. Is this a usual request?

This can happen if there was a transmission error during  the import or the issuer had electronically formatted   this information  in a way that was incompatible with the TurboTax program (e.g. sometimes SSN are represented with dashes and sometimes they are not).

Were you able to add (or correct) this information in the W-2 interview or Review screen? If not, you may have to delete the Form W-2 and manual enter it in the W-2 interview.

See: How do I delete forms in TurboTax Online?

After deleting the W-2, log out of the program. When you log back in, you use the Delete a Form tool to see if the W-2 has been removed from the list of forms in your return.

Why does this happen? Once you enter (or import or transfer) certain information, the program creates or updates forms and worksheets that use that information. In many cases, you cannot "change" that information in the interview process - in a manner of speaking, it has been "written in ink" on the forms. You have to delete the form and any associated worksheets in order to correct.