I had the same issue. I had never been a problem in the prior years until a recent update to my desktop version. This is a Turbotax software bug - checking the box for 3520 doesn't mean 3520 will be e-filed together with 1040; it just indicates on 8938 that a 3520 form will be filed with the IRS (by post).
Please fix this bug in your next version. Or I will have to switch software.
