When I first install/configure W3TC to use Amazon CloudFront as a CDN, everything works fine (well, mostly, but we'll deal with the minor issues later.) The majority of images/css/js files are offloaded to the CDN. The files are uploaded to the CDN and the URLs are being rewritten in the HTML to point to the new location.
Sometime later (sorry, but I don't have a specific timeframe), the site reverts back to being almost entirely served locally. A few items are still offloaded, but most are not. The files are still located on the CDN, but the URLs are no longer being rewritten. They point to the local copies.
What could be going on? Where could I look for further info? The "Unsuccessful File Transfer Queue" has a large number of entries, but they all read "Last Error: Object already exists", which doesn't suggest to me a true problem. The Delete Queue is empty. The wp-content/w3tc/log/ folder is empty.
Thanks for your help!