I noticed a few days ago that I'm not getting my logwatch emails to the root account any longer, and while I've definitely been applying updates from base, no other changes have happened on this box.
I ran logwatch at the command line:
logwatch --detail medium --mailto root@fqdn.example.com
but still no email.
Try sending it to an email outside of your domain like mytest@gmail.com or whatever your mail is. More than likely you reset or started some kind of program like spam assassin. There are enough bad ips, urls, etc to just make it get killed by spamassassin or any other kind of software for mail.
Try whitelisting it in procmail or whatever you are using.
Worked for me