This was reproduced with NO adblock on Google Chrome running on a OSX 10.12.1.
The poll did appear initially in the Pietro thread, but a few hours later it was gone. That was the first instance where I saw this happening, then later noticed the problem with the Music Polls thread.
Note that when the post which contained the poll is quoted, the unformatted poll options appear in the quote, showing that the composite elements are still there, they're just not being rendered.
I can't see anything similar on Discourse unfortunately, which makes me suspect it may be due to the custom configuration of the site and its ads.