[tor-relays] Hash of session info was not as expected

[Logforme]

My tor log file is usually quite boring but today it looks like this:
Jun 14 13:42:46.000 [warn] Hash of session info was not as expected.
Jun 14 13:57:56.000 [warn] Hash of session info was not as expected.
Jun 14 14:11:58.000 [warn] Hash of session info was not as expected.

A new line about every 10 minutes since  04:14:53 (CET)

Is it a user with problems, an attack on my relay or a sign that my
relay have some kind of hardware/software issues?