Interesting, it seems the arrow isn’t displaying, causing the spacing issue.
In “Appearance > Menus”, is this menu designated to the “Secondary” theme location?
If so, can you try #1 on this page to see if there’s a plugin conflict?: https://generatepress.com/knowledgebase/debugging/
The code adding the arrows to the primary navigation is the exact same as the secondary, so I wonder what’s stopping it from working.
Let me know 🙂