Categories page does not show all correctly assigned posts

Hello, All posts that I have assigned to my “Articles” category should be listed on this page: https://jevondangeli.com/articles/
I have several other posts that are equally assigned to the “Articles” category and have all other settings that I can see under “edit post” the same than those that are showing up – but they don`t.

Using the search function for a particular article′s name on my site, it is correctly being called up by the search and shows the green “Articles” category underneath the post′s heading. It is however not showing up on https://jevondangeli.com/articles/

Example: A search for “Overcoming Mental Obstacles” on my site calls up 4 articles in this series, however on https://jevondangeli.com/articles/ only my Overcoming mental obstacles for kids & adults article is listed, not part 1, 2 and 3.

Aside from checking if any settings in the edit post section are different for part 1, 2 and 3 (compared to the post that shows up under the articles category), I have gone to permalinks and clicked on “save” without making any changes. I have re-selected the articles category for each post and republished.

Any hint what to check next would be greatly appreciated.

NB. jevondangeli.com is a clone of a previous site. It seems as if not all of the posts are being recognized as being assigned to the articles category, even if the physically show in the editor that they are…

The page I need help with: [log in to see the link]