Snapshots Are Successfully Created, but Not Uploaded (to S3-Compatible Storage)

I have used Snapshot Pro in the past to upload backups to S3. I am currently attempting to configure Snapshot Pro to upload backups to Wasabi (an S3-compatible storage provider). However, the snapshots are created, stored locally, and then show as "uploading, but the upload never completes. I have tried this with a relatively small backup, and the same thing occurs (the upload should be nearly instantaneous on this server); so the issue is not the size of the backups.

If needed, I can provide access to the server and any helpful logs to support.