This might be related to https://bugs.launchpad.net/swift/+bug/1805227 -- you might want to try enabling force_swift_request_proxy_log or just grepping your object-server logs for the DeleteMultiple transaction ID (tx5e61bcccea464480b4cc7-005b184a52). If I'm right about the bug, I'd expect a bunch of HEADs that all 404, so swift3/s3api never follows through with the DELETE.
Yes, it should. That's the purpose of the HEADs -- to figure out whether the object is a multipart upload (in which case the [Swift] DELETE request should include a ?multipart-manifest=delete query param) or a regular object.