Menu Expansion Settings

I’m using Drupal 8 (latest version) on a just installed Lightning site.

I can’t remember where this setting is, but I’ve got menus with submenus. Although I’ve set them to automatically expand if they have submenus, it’s not happening. It’s been some time, but I seem to remember that there’s a setting somewhere that needs to be altered to allow this to happen below level 1 menus.

Can someone help me to find this? I can’t think of any other reason why my submenus don’t automatically expand to show subitems.

If it matters (and I don’t believe it does, I’m using Aegan theme, but it seems to be true for the default theme as well.

Thanks.

Drupal version: 


Source: https://www.drupal.org/taxonomy/term/22/feed