Aparently Instagram have changed the shared data. You can fixed temporarily modifing next lines (until the new version of this plugin)
In the file instaram_slider.php in v1.4.1
line 993
$entry_data = isset( $results['user']['media']['nodes'] ) ? $results['user']['media']['nodes'] : array();
replace with
$entry_data = isset( $results['graphql']['user']['edge_owner_to_timeline_media']['edges'] ) ? $results['graphql']['user']['edge_owner_to_timeline_media']['edges'] : array();
line 1005
if ( 'hashtag' == $search ) {
replace with
if ( 'hashtag' == $search || 'user' == $search ) {
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