I had exactly the same issue. I also tried customer care and their solution after a couple of hours on calls with various tech people was to switch to the desktop version which I will not do.
So I entered them one final time, immediately downloaded the draft version of the tax return from the print center - this includes the 8938 forms I had just entered before TT online deletes them yet again. I plan to file electronically without 8938. Then I will file form 1040-X by mail to add the 8938 forms manually. It has been a huge waste of my time.
