That might depend on when the site was created, and how busy the site is. Logs are rotated when their size is larger than a preset limit (100 meg).. or when the monthly reset occurs. That monthly reset alone should have caused the log to rotate, but it won't rotate if the logs are empty. One things that could happen is some hosts move the location of the logs which will confuse DirectAdmin when it goes to do the rotation. If you want, you can send an email to support@directadmin with the domain, admin and root info.
I've found that all rotated logs are emty. For admin, reseller and all users there are files like
-rw-r--r-- 1 root root 45 Oct 1 00:20 Sep-2003.tar.gz
-rw-r--r-- 1 root root 45 Sep 1 00:20 Aug-2003.tar.gz
-rw-r--r-- 1 root root 45 Aug 1 00:20 Jul-2003.tar.gz
We have our own log rotate system which rotates based on either size or time. The size is specified in the admin panel, and "time" is on the montly reset: first day of the month.
The only reason I can think that they might be emtpy is if the logs are either empty, or tar didn't have the proper privileges to read them.
I've looked over the code and noticed some inconsistencies between the 2 backups, one uses root, one uses the user, but since it's a root owned directory, the user won't be able to write to it. But, that doesn't explain why the are files there .. I'll change the code to use root for both circumstances and hopefully that will work.