The NL symbol, U+2424, is supposed to appear in text as the two small letters N and L, just as it appears in a Unicode chart. But instead you show it as an actual new line, like this:  (This shows as beginning a new line, but it should look like these others in the same category: ␠ ␡ ␢ ␣. Only U+000A should actually start a new line.
Testing …  maybe there is a bug in nokogiri…
Seems to work just fine here
Testing .... ␤ maybe there is a bug in nokogiri...
「いいね！」 1
I am not sure what exactly is being reporting here? Are you saying email versions of the posts, as delivered through email notifications, have this?
Yes I can repro this, the workaround for now is to use ␤ instead.
@Vitaly this appears to happen in https://markdown-it.github.io , do you know if this is on purpose in the engine? It does not happen in dingus: commonmark.js demo
「いいね！」 3
テスト中… ⋒ 行はここで終了 →
これは修正されたように見えますが、@sam？
はい、nokogumboを導入したことで、この問題やその他の類似の問題が解決されました 
「いいね！」 1