There is one thing I just noticed as far as the meta_query goes.
First of all, if you’re field is not returning an ID of the “ct_industry” assuming that this is some type of relationship field, then you need to get the unformatted value.
Secondly, since you are searching for numbers in a field that contains arrays then your LIKE needs to be altered.
All of the following are guesses assuming that “ct_industry” is either a taxonomy or a relationship field.
$relatedCat = get_field('service_related_industry', false, false);
$args = array (
'posts_per_page' => 3,
'post_type' => 'case_study',
'meta_query' => array(
array(
'key' => 'cs_industry',
'value' => '"'.$relatedCat.'"',
'compare' => 'LIKE',
)
),
'orderby' => 'DESC',
);
if (!$relatedCat) {
$relatedCat = get_field('service_related_category');
unset ($args);
$args = array (
'posts_per_page' => 3,
'cat' => $relatedCat,
'orderby' => 'DESC',
);
}
as far as why it’s returning the wrong number of posts, yes, a pre_get_post filter added somewhere else can alter the settings of any query done anywhere and any time https://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts
