Is it possible the password used to connnect to the LDAP server changed or expired? Those are fairly common reasons that a profile breaks. Other possibiliities are firewall changes or server changes that no longer allow the connection through.
I forgot to mention that was already checked and we've verified that the LDAP password was the same. What I was trying to find was a reason, it seems to me like it should be a connection issue that last long enough to trigger the alert. But I couldn't find a log to confirm what actually happen.