Thanks for looking into this and prompting me to look into it further. I’ve solved the issue now and will post here in case it will help @lpb and anyone else in the future.
After some testing in my browser (Chrome), Chrome Incognito, Firefox, MS Word, and another computer (same Chrome version, and it worked), I came to the conclusion that it is an issue only on my computer and not limited to Chrome or Asana.
A bit of a Google for other people having problems with Ctrl-Shift-8 led me to a post that suggested checking Chrome extensions: “Load chrome://extensions. Then from the hamburger menu choose keyboard shortcuts. Just reset them for the extensions you want to map.”
That was exactly the issue for me - an extension called “Hangremote” had mapped exactly Ctrl-Shift-8 and Ctrl-Shift-7 for some shortcuts, PLUS had made Ctrl-Shift-8 a global hotkey I set it to something else and I am back to being able to use those key combinations as normal now. It could be something else for you @lpb, but likely something is overriding the hotkey combination, so at least you have a direction to look in now.
I realised today how useful that shortcut is to also turn selected lines/paragraphs into bullet points, so creating single bullets would only have “solved” half my problem. Thanks again for your input everyone.