Hey, I see that you changed write function. But on some pages (including -  /light-sensor) the uploading path is incorrect now. And code editor got broken because of this. I don't know if have you changed it or not, maybe you made some extra changes to .html file or something?
The uploading link looks like this: <script src="/s/lsc-ace-serial_and_arduino-mode-combined.js">
//This script allows the IDE to function
</script>
but it can't find and upload file from this directory.
On the page /learn-play-3-tones-to-a-speaker the path is different:
<!--<script src="/s/lsc-ace-serial_and_arduino-mode-combined.js">
//This script allows the IDE to function
</script>-->
<script src="https://s3.amazonaws.com/compile-script-9-13-18/lsc-ace-serial_and_arduino-mode-combined.js"></script>
it uploads from s3.amazon and monitor works there, but old link is commented out. To make it work, the uploading link should be changed to https://s3.amazonaws... .
To test this script on /learn-play-3-tones-to-a-speaker you must show monitor button there, you can do it by typing command in console of devtools - " document.getElementById('monitor-button').style.display = 'block' ". It works for sure.