Today (1 February 2022), at around the time when this chess question was first posted, the PGN Viewer plugin stopped working across the whole site. The issue seems to be reproducible on all devices and browsers.
Instead of the chess diagram, we now see a code block with the chess notation instead:
There is a console error on all pages of the Chess SE and Chess SE Meta websites:
There is also a question about this on Chess Meta SE: Why has the PGN Viewer (replayer) stopped working?