It should be accepted. Please report it.
Note, however, that short adverbs of frequency such as "often" are usually put before the main verb (or after it if the verb is "to be") or at the end of the sentence. Reference: https://dictionary.cambridge.org/us/grammar/british-grammar/often
• Scrivi spesso ai tuoi genitori?
• [ Do you often write to your parents? ]
• [ Do you write to your parents often? ]
P.S. I'm not inclined to try "Do you often write to your parents?". For a start, I typed "Do you writen to your parents often?" on the first try. The other reason is that I am more interested to learn the expressions in Italian.
Duolingo usually requires the auxiliary verb "to do" in questions (in this case, "Do you write often to your parents?"). Notice that it is required in formal speech and optional in informal speech.
Also notice that, although "you write often" is correct, the most usual position of "often" is before the main verb (in this case, "you often write").