You might see a sudden increase in your feed traffic in the next few days. Please be happy that there is nothing wrong with our stats system and all that traffic is genuine. You might see this sudden plunge in subscriptions and traffic to your feeds as we are broadening the coverage of User Agents. This is a routine at the backend to include in our stats system the new User Agents from time to time as they become more popular to track subscriptions and hits from them.  However, this time around there are more than a few User Agents that we are adding to our database and this might make your graphs surge a little if your users are using these agents. Also, for the few users for whom the Google Reader subscriptions were not showing up, the good news is that this is now fixed and you should be able to see the subscriptions and hits coming from the Google Reader to your feeds.
Cheers