Plugin stopped working: cURL error 28

This plugin was working great until I updated to the newest version and it stopped working. (We also launched a new version of the site, though, on the same server.) If I go to the settings page I see this:

There was an error attempting to check the permissions of the bucket ******: Error retrieving credentials from the instance profile metadata server. (cURL error 28: Connection timed out after 1001 milliseconds (see https://curl.haxx.se/libcurl/c/libcurl-errors.html))

If I click on the ‘change’ link next to the bucket, I see this error:

Error fetching buckets — Missing required client configuration options: region: (string) A "region" configuration value is required for the "s3" service (e.g., "us-west-2"). A list of available public regions and endpoints can be found at https://docs.aws.amazon.com/general/latest/gr/rande.html.

Any ideas on how to fix it?