What
Before uploading, the client announces the upload. That announcement can clash with a record that already exists, because the step is only allowed to create a new record and never to overwrite one. When this clash happens, the client now reads its own journal (readOwnJournal). If that journal was written using the same announcement token, the client takes the journal's etag and carries on. An etag is a label that identifies one version of a stored file. Before this change, the client gave up.
Why
An upload whose earlier attempt already got through no longer fails just because that first attempt's record is still there.