I have not had a false positive situation occur like this before. There could be a couple reasons the error did not appear in the logs. The logs on Tableau Server had not been cleared at all? Some customers run weekly or daily log cleanups up to help manage disk space.
Additionally, I am curious what the error was that was stated in the email address? If possible a screenshot of the error in the email would be great.(As this is a public forum, please make the screen shot is of non-sensitive data)
Hope this helps!