We experienced a few dozen unrecoverable files on Rackspace Cloud Files (which at the time used Openstack under the hood). This is out of about 10M objects that totaled about 2 TB, but they were less than 3 years old. The API call just failed with a 404 even though the files were listed in the list API call.

The corruption was uncovered when we started migrating to another cloud platform, we had to restore from local copies.