It happened again (this time with just a new autosave that I don't care about), at least I think this is the same error:
<Error>
<Code>AccessDenied</Code>
<Message>Access denied.</Message>
<Details>
Anonymous caller does not have storage.objects.get access to the Google Cloud Storage object. Permission 'storage.objects.get' denied on resource (or it may not exist).
</Details>
</Error>