After upgrading a customer's site from CE 220.127.116.11 to 18.104.22.168, FedEx no longer returns any rates at checkout. Everything is set up correctly, it worked great prior to the upgrade.
On SO, I noticed someone corrected this by replacing
with the version from 22.214.171.124, but I wasn't comfortable with it.
I didn't find the answer elsewhere on the Internets, so I decided to share it here.