SE Bots Activity Log

Looking through my SE bots activity logs, and lots of days had no bot activity whatsoever. However, when I looked in my server logs, I see tons of bot activity for those days. When I look in the /vbseo_sitemap/data/hits directory, this is what I see:

-rw-rw-rw- 1 board board 1771 Jul 11 23:59 20110711.log
-rw-rw-rw- 1 board board 0 Jul 12 01:02 20110712.log
-rw-rw-rw- 1 board board 1892 Jul 13 23:59 20110713.log

Notice that the middle record (July 12, 2011) has a last write time of 1am, whereas the other two records were last written at 11:59pm. What would cause this log file to not be updated for an entire day (resulting in a blank entry in the SE bots activity log report)?

Thanks. I'm trying to chase down a huge drop in traffic, so I'm trying to research anything out of the norm I can find.

That simply says that nothing happened that day, at least with a matching mime/ip/etc that would record a record.

It's possible your site was down, or no bots came that day.

That's the thing... my site wasn't down and bots did come that day (I see them in my access_log and they successfully crawled forum pages). The log file for July 12th is not standalone; I see at least 20 more of them (not in a row) whose last mod time is around 1am.

Any other guesses?