In my experience, the return will e-file without that info and the IRS holds the return and sends a notice asking for the information that was missing. 

If the return is rejecting, look for something in the worksheets that indicates the taxpayer has a 1095-A. There's a box somewhere that needs checked or unchecked.

 

It seems like many people signed up for marketplace insurance without realizing it (most thought they were just getting a quote).
Have you client call healthcare.gov and see what they have on file for their SSN (or any SSN on the return).