How did you understand then it fails to upload? By checking S3 directly?

It's very strange that S3 didn't write anything to log. Did you check Jenkins log as well?

p.s. Can you provide s3 settings? (for this job and global one and don't forget to remove sensitive data )

the buildnumber folder doesn't get created in S3, is the outcome I found it because a later job that deploys to AWS fails because the artifacts are missing.

Things that may be relevant but not sensitive include:

job settings:
Storage class - Standard
Bucket Region - us-east-1
No upload on build failure is checked
Manage artifacts is checked
no other options are checked

Did you check jenkins log?

Something is missing here. A lot of stuff was fixed (flatten directories, fingerprints, "keep structure" in global configuration) since 0.8.

Same here:

Jenkins 2.25 / S3-Plugin 0.10.10

The publish process keeps running and does nothing:

Publish artifacts to S3 Bucket Build is still running
Publish artifacts to S3 Bucket Using S3 profile: jenkins@xxxxxxxxxx
Publish artifacts to S3 Bucket bucket=xxxxxxxxx.s3-eu-central-1.amazonaws.com, file=xxxxxxxxx region=eu-central-1, will be uploaded from slave=false managed=false , server encryption false

using the S3 profile creds from aws cli works just fine.

Try to upload from slave, it's common setting in both failed cases.
I will check how uploading from master differs from uploading from slave later.

I got it running. I reentered the aws s3 creds in the jenkins configuration, mysteriously they were empty.

I have a similar issue.
Jenkins 2.36. S3 Plugin 0.10.11.
Bucket Region is eu-west-1

My slave is running on AWS with IAM profile which enables publishing to S3. So no credentials are required.
When the manage artifacts is not checked, the artifact is uploaded successfully.
When the manage artifacts is checked, the artifact is not uploaded at all and no error message is reported. But, when drilling down to the "Last Successful Deployed Artifacts"

This XML file does not appear to have any style information associated with it. The document tree is shown below.
<Error>
<Code>AuthorizationQueryParametersError</Code>
<Message>
Error parsing the X-Amz-Credential parameter; the region 'us-east-1' is wrong; expecting 'eu-west-1'
</Message>
<Region>eu-west-1</Region>
<RequestId>CFC02E45B5802788</RequestId>
<HostId>
MX0ahVKKzXrJWovhhgDpabz1hGrBi5LjKh+RkpW6liy/1vK/zMe9Is6ZfexoZJCp7xhLQ4HPmVg=
</HostId>
</Error>

Build log:
10:05:14 Publish artifacts to S3 Bucket Build is still running
10:05:14 Publish artifacts to S3 Bucket Using S3 profile: Publish
10:05:14 Publish artifacts to S3 Bucket bucket=sb-current-build/unstable, file=sparkbeyond-RC-5273.run region=eu-west-1, will be uploaded from slave=true managed=true , server encryption false

same issue here:
Publish artifacts to S3 Bucket bucket=-***, file=app-debug.apk region=eu-west-1, will be uploaded from slave=true managed=true , server encryption false

Error parsing the X-Amz-Credential parameter; the region 'us-east-1' is wrong; expecting 'eu-west-1'