This is something related to the content of the post. Something is messing up the Mardkown created for internal Pandoc conversion to HTML and this creates a parsing errors leaving some ::: {.cell syntax unparsed.
To look closer, we would need to see the content. Do you have a repo we can access ?
Also, this may have been fixed in a recent Quarto version. Which one are you using ?
1.5 is now the latest, and you can also try the 1.6 pre-release.