What do repeating '^@' symbols in a logfile mean?
I believe that these are NULL (0x00) characters. Just from the segment of the log file that you have presented, looks like a reboot. It is possible that the buffer to be written out to the logfile was a little corrupt due to the stopping of the kernel logging daemon while attempting to write out something. This is only an educated guess however.
Summary: I'd not be overly converned from what I see here.