Broken node edit layout for landing pages with Gin theme and no Save button

Problem/Motivation

We are using Gin as the admin theme for content and on the landing page node edit screen the layout is broken.

There are no Preview or Save buttons and thus it is not possible to save an existing landing page. The issue doesn't occur when creating a new landing page node.

It only happens on landing pages, and the layout is expected when using Open Social as the content admin theme.

Steps to reproduce

Use Open Social v12.4.2.
Turn on Gin as admin theme for content: "Use the administration theme when editing or creating content"
Edit a landing page to see the issue (see screenshots for an example)

Proposed resolution

I can see that this is caused by the custom template "social_landing_page/templates/page--node--landing-page.html.twig", which I would imagine is not relevant if using the Gin (or any other) theme to administer content?

Remaining tasks

User interface changes

API changes

Data model changes