It seems there is something wrong with the text positioning on MSE site (seems alright on other sites as far as I've tried, including mathoverflow.net). Specifically if you type the following text in post/comment, you can see the issue:
Some other text around 3366 and more text.
It does not happen for numbers typeset in math mode (
$$). I can see this result in Chrome and Microsoft Edge on the desktop. It looks alright in Chrome when viewing on the phone.
By the way the original scenario when I encountered this was referrence to OEIS sequence A333666. Looking at how OEIS sequences names are typeset on the site, this seems like a corner case where people use both styles (text and MathJax).