I've been trying to add variables to templates since yesterday. I'm on a Mac and have now tried in three browsers: Chrome, Safari, Firefox. It doesn't work. I can add the new variable in edit mode and everything seems fine, but when I create a page using the template, the variables aren't there at all.
The new Editor experience has changed this. Variables in templates no longer seem to work when a page is created using that template. This has been reported. https://jira.atlassian.com/browse/CONFCLOUD-66456.
We have only just moved to the new Editor experience and I encountered this yesterday when a user complained that their new checklist button had changed. It was because of this. As the template only had three variables, I just deleted them and modified the instructional text accordingly. Not ideal, but I also explained to the user that vendors changing stuff is part of the deal of using Cloud, and beyond my control. Hopefully, variables will return one day.