See: https://bugzilla.redhat.com/show_bug.cgi?id=1164038 The new AWS Frankfurt region requires an updated AWS-SDK library. However, this dependency was not discovered until very late in the testing process. As a result, the AWS-SDK library was not updated for the 5.3.2 release. The 5.3.2 release includes an extra "Region" option for "Frankfurt (EU)" when adding an Amazon provider. This region should not be selected in the 5.3.2 release. If selected, the CFME appliance will indicate that the "Login failed due to bad username or password". The current work arounds for this bug are: 1) Avoid using the Frankfurt (EU) region when adding a new Amazon provider. Or, 2) Manually update the AWS-SDK gem on an appliance. Option (2) is an advanced operation and is not recommended for typical users.
Verified and confirmed that the document is updated with the details mentioned by Greg in https://access.redhat.com/documentation/en-US/CloudForms/3.1/html-single/Management_Engine_5.3_Release_Notes/index.html#chap-Known_Bugs . Hence moving it to verified state.
The requested change is now live on the Customer Portal. Closing.