I’m noticing this exact same problem with “{{unknown}}” showing up on the homepage as the first word of the first sentence of a post. Just like others here have described, when I click into the post, it goes away.
It makes the homepage look horrible. I’ve tried to come up with a workaround, but nothing I’ve tried seems to help. In the text editor, there is nothing to indicate why this is happening, and it looks fine in the preview. I hope someone figures it out soon. Thank you for your help. ??