I don't actually use it, so I'm not sure how it works, sorry about this! I tried testing it out again, and it's coming out blank for me as well. I think it could be something to do with the embedding code, because if you click edit again the entire code disappears. So it might be something between Google and Dreamwidth right now? Maybe the old codes that worked before is why it still works in some posts now, because they haven't been edited.

EDIT: yeah i tried it a couple of times again, even making a new one, and finding a preexisting code to see how it goes, they all go blank. I think this one probably needs you to send in a support ticket to Dreamwidth cos they might know why, it could be the latest code push.