Please update the following in the ( index-post.php ) file for the following reason below.

Please replace this below:
<?php if( is_date() || is_search() || is_tag() || is_author() ) { ?>

with this below:
<?php if( is_date() || is_search() || is_tag() || is_author() || is_category() ) { ?>

Because the preference is that the category pages display excerpts instead of the full blown articles on the category listings.

When I run the Blog MU update, it wipes out my edit for the category excerpts and I have to fix it in multiple sites.

I thank you for your time and consideration of this requested Blog MU change.