You might be missing the ‘meta_key’ arg here:
$args = array(
'ignore_sticky_posts'=> 1,
'meta_key' => 'wpl_location', // here
'post_type' => 'post_projects',
'meta_query' => array(
array(
'key' => 'wpl_location',
'value' => 'Europe',
'compare' => 'IN',
),
),
);
source: https://codex.wordpress.org/Class_Reference/WP_Query (about three quarters down the page).