I'm having the very same issue but I could not get any help
If I put a "read more" in the middle of the article text, the introtext is displayed in the homepage, but if you open the article you find the introtext twice. So I have to put the "read more" at the very top of the article, but this way I don't have any introtext in the homepage.
The strange thing is that in the template example article the very same way to use "read more" does not cause that issue; yet both articles belongs to the same category.
If I publish an old article (contained in the example data) it behaves correctly, but if I create a new article the problem arises. I could not see any apparent difference between the two articles (mine and the example one).
Thanks for your help.
PS I updated the template to Decor v.2.0.0 but no change...