The problem seems to be clearly in that new username length validation in turbotax.
Fidality allows usernames with 6-15 characters. Turbotax requires it to be at least 9 now (worked with shorter usernames last year).
Mine username was 8 character long. I workarounded that problem by changing my username in Fidelity. Now it's longer than 8 characters and I can use it in Turbotax.
