Cannot set "Alternate Region host" in AWS region

We have configured Snapshot Pro on our sites to backup to Wasabi (it's an S3 compatible storage). The test works fine and I can see the snapshot file. But when we do an actual snapshot, it stalls uploading the file and there is nothing uploaded to Wasabi.

In my "Amazon S3" type destination, I set the "AWS Region" to "Other" and tried to set the "Alternate Region Host" to "s3.us-west-1.wasabisys.com", but it doesn't save. I think there's a bug in this field, it doesn't matter whatever value I enter here, it doesn't save.

Please advice.