I think actually the bug might live within the function coauthors_posts_links() caused by the co0author plus plugin. I will check with the developers of the plugin and come back if needed.
Hi! What I’ve got from deleting ct_mission_news_post_byline from content.php is shown in the screenshot; it completely erases al author, co-author, and publishing date information. Nothing occurred in the post by deleting the same function from content-archive.php.
Since Mission News Child uses also Mission News as parent theme, the function in question in the parent theme in the functions.php is difference from the function in the in the Child theme in the functions.php. I also leave screenshots of each the parent and child theme functions.
I tried commenting one function and leaving the other, and vice-versa, and the one with better format and not repeating names of author and co-author is leaving the function int he parent theme uncommented. So, I got rid of the function in the child theme, but the names do not appear with links to their archives pages.