Ceph - After 2.3 upgrade RadosGW errors with 404 on some DNS names

Issue

After upgrade from RHCS 2.2 to 2.3 RadosGW is no longer serving some of our DNS names (endpoints). We receive the following error when accessing some DNS names via s3cmd:

ERROR: Bucket 'my-bucket' does not exist
ERROR: S3 error: 404 (NoSuchBucket)

In the RadosGW log we see a http error 404:

2017-06-28 08:14:40.735428 7ff88cd9f700  1 ====== req done req=0x7ff88cd99710 op status=0 http_status=404 ======
2017-06-28 08:14:40.735470 7ff88cd9f700  1 civetweb: 0x7ffa180083c0: 192.168.11.23 - - [28/Jun/2017:08:14:40 +0000] "GET /my-bucket/ HTTP/1.1" 404 0 - -