IRS says:
Reasonable Cause Exception
No penalty will be imposed if you fail
to file Form 8938 or to disclose one or
more specified foreign financial assets
on Form 8938 and the failure is due to
reasonable cause and not to willful
neglect. You must affirmatively show
the facts that support a reasonable
cause claim.
The determination of whether a
failure to disclose a specified foreign
financial asset on Form 8938 was due
to reasonable cause and not due to
willful neglect will be determined on a
case-by-case basis, taking into
account all pertinent facts and
circumstances
