It only works if you start typing 'tm1' and there is a space before this. So as an example, if you start by '<', then proceeded to type 'tm1' then the list will not show.
Another possibility is, the version of your VSC. I have tried the above on a 1.8.1 version. If you have an older version, try updating your VSC:
Do let us know if this was your case or if the above helps.