Here are two more vanishing 12-plets similar to yours:

$$
\substack{
\displaystyle{◻◻◼◻◻◻} \cr
\displaystyle{◻◻◻◼◻◻} \cr
\displaystyle{◻◻◼◼◼◼} \cr
\displaystyle{◼◼◼◼◻◻} \cr
\displaystyle{◻◻◼◻◻◻} \cr
\displaystyle{◻◻◻◼◻◻}
}
\quad
\substack{
\displaystyle{◻◻◼◻◻◻} \cr
\displaystyle{◻◻◻◼◻◻} \cr
\displaystyle{◻◻◼◼◼◼} \cr
\displaystyle{◼◼◼◼◻◻} \cr
\displaystyle{◻◻◼◻◻◻} \cr
\displaystyle{◻◻◼◻◻◻}
}
$$

I found these using [JavaLifeSearch](http://conwaylife.com/wiki/JavaLifeSearch), combined with manual filtering of the search results to skip any non-polyplet patterns.  Unfortunately, since the tools I used aren't really designed for this specific task, I cannot absolutely guarantee that there aren't any other 5–12 cell vanishing polyplets that I've somehow missed.