when using a fresh development environment following the steps here:
when you go to /admin/config/emoji clicking on “Settings” “Add emoji” does not load the pages, this requires a page refresh after clicking the links.
With the page refreshed Settings shows and Add Emoji shows.
When you add your first emoji it redirects to /admin/config/emoji and you cannot see the emoji just added, you have to refresh the page.
Once refreshed you can see your first emoji uploaded.
When you try to upload a second or any additional emojis even refreshing the /admin/config/emoji page no emojis are shown so you can no longer manage uploaded emojis even though they usable throughout the website.