There have been notes and I have seen it that some users posts that are filtered but not shown as filtered. Here is an example of such a post that seems reliably to reproduce that.
Seems one way to get a post that is filtered but not detected as filtered by the extension is to post a URL. That does not show up in another browser nor even causes the “1 new post” message to appear. So not sent onwards by LF to other users but is sent back to you to put your own post on the page.
Like this but unencoded: 𝗐𝗐𝗐.𝗇𝖻𝖼𝗇𝖾𝗐𝗌.𝖼𝗈𝗆/𝗇𝖾𝗐𝗌/𝗎𝗌-𝗇𝖾𝗐𝗌/𝗐𝖺𝗌𝗁𝗂𝗇𝗀𝗍𝗈𝗇-𝗌𝗍𝖺𝗍𝖾-𝗐𝖺𝗇𝗍𝗌-𝗋𝖾𝗌𝗍𝗋𝖺𝗂𝗇𝗂𝗇𝗀-𝗈𝗋𝖽𝖾𝗋-𝖺𝗉𝗉𝗅𝗂𝖾𝖽-𝗇𝖾𝗐-𝗍𝗋𝖺𝗏𝖾𝗅-𝖻𝖺𝗇-𝗇731216.𝗁𝗍𝗆𝗅