I've just noticed the Dependency style option in "view settings" (FYI - am trialing the new header style...in case that matters) But changing it to Lines from Badges doesn't seem to make any difference to the view. I was hoping this would evoke lines between the dependent issues on the Timeline. If not, what is it supposed to do?
The dependency lines will be visible if the dependent issue is also in the plan. For instance, if you have a dependency on an external issue or an issue that is filtered or it is in another group (in case your plan is grouped by something) then instead of a line, a link icon is shown.
For more information about the new feature, take a look at our docs.