Hello @OF4,
In the first issue I could reproduce the issue in this post. Could you check you have the correct resource in the bucket policy it might be missing the correct parameter (should look like this: "arn:aws:s3:::<YOUR-DATA-BUCKET>/csv/*" to work.
In the second issue after you run a new notebook for a second time the AWS has the previous credentials. Just logout and click the link again to fix it:
