OK. Here is what one of the Admins said:
We didn't change anything in the forum recently. So it should be related with Edge update.
However, there is a quick solution for that. You know the little icon at the top of the posting panel (icon A letter "Switch Editor to Source Mode"). If member clicks on that icon and switch to source mode while pasting the script and then switch back then it should work without problems. I have no chance to test it but it should work. Temporarily disable WYSIWYG and paste the script, that's it.
Though the "easiest" solution probably would be to install Chrome.