Google Analytics stopped gathering data on some of my sites on May 2. I didn't realize it until today. It appears that the sites that failed are those that I upgraded WP-HTML-Compression. Google reports that the tracking code is not installed.
When I turn off the Compression plugin then Google is able to see the tracking code properly again.
I use Ultimate Google Analytics to insert the GA script into the sites. That appears to still be working as I can see the script in the source code. So I'm not sure why it fails with WP-HTML-Compression running unless this plugin changes something within the script.