It sounds like the plugin expects there to be a get param.
Your rewrite-rule is removing the get-param before it can be used by the plugin.
If the plugin hasn’t been updated for a long time (it’s abandonware) then you can go through the plugin and replace the get-param with the portion of the url which would have been the get-param. Just make sure to prevent the plugin from updating after you’ve made your edits.
If you add the following
function custom_add_rewrite_rules() {
add_rewrite_tag('%query%','([^&]+)');
add_rewrite_rule(
'^something-here/([\d]+)$',
'index.php?p=10219&query=$matches[1]',
'top'
);
}
add_action('init', 'custom_add_rewrite_rules');
& then replace
$_GET['query']
&/or $_REQUEST['query]
with get_query_var( 'query' )
in the plugin you’ve described, that should be enough to do the trick.