Note that if you have a child theme that uses Mantra as the parent, and you have added ‘mantra_comment’ in your child theme’s functions to override how Mantra displays comments, you have to modify their base ‘mantra comment’ to include a new ‘case statement:
switch ( $comment->comment_type ) :
case '' :
case 'comment': // add this line
This ‘bit’ me because my modified mantra_comment overrode the fix that Mantra installed to fix the bug in their original ‘mantra_comment’ function. Adding the above fixed the issue of comments not displaying in my child theme that uses Mantra as the parent – my implementation of the child theme used ‘mantra_comment’ from prior versions.