Default community comments to show all replies "Show All Replies" 

By default, it is hiding some replies in the comment section

This is the default configuration for the widget "Community Comments"
https://instance-name.service-now.com/sp_widget.do?sys_id=d4a6586c674132007bf09a6617415a31

If you are using the OOB widget > look at the Client controller of the widget > Check on line 35
==> c.showAllReplies = false; //If True, shows all the nested replies expanded on page load.

Review the above widget and the line above which sets c.showAllReplies = false

As per widget, you can set this to true to show all the nested replies expanded on page load