I'm using 1.6.9 (upgraded from 1.6.6 because I was seeing the same problem).  I have it running on 8 different servers at different locations, some are SMP, some aren't.  On these hosts, we have anywhere from 2 to 14 devices logging to the servers, some via 514/tcp, others via 514/udp.  All of the loggers typically sit with a load average < 1 (usually not even registering), and a cpu idle of 99%.  7 of these remote loggers also log to our local machine, but only 5 lines every 2 minutes (for stats). 

What I've noticed (and I've seen this on all of them at one time or another), is that syslog-ng just stops.  ps shows it running, but the log file (/logs/messages) never changes.  If I tcpdump on the interface that it's listening on, I see traffic, and it seems that the act of tcpdumping causes the log file to start to grow again, then a little while later, it may stop again.  It's sporadic though, on one of my systems, it hasn't done it in over 2 months, on another, it's done it 3 times today.

I've pulled out my last hair and still haven't come any closer to a solution.  I've recompiled the source, loaded 3 different versions, etc.  The only thing common is that all of these systems are running RHEL3.

Any help would be greatly appreciated.

Thanks,
Tony