This issue is platform related. Affects only macOS.

Steps to reproduce
1. Create the new article, for e.g. Article A. In the intro add a heading, for instance, H3.
2. Create the second article. In the body embed Article A.
3. Go to the front page.

Expected result
Normally rendered heading.

Current result
In dev mode, see attachment 1. For prod mode see attachment 2.

Additional information
The customer noticed a bit different behaviour, on his installation heading tag was rendered as: <h1>Hello World</h1>.