Warning: Illegal string offset message

Website using the plugin: http://clentparishcouncil.gov.uk
WordPress Version : 4.9.8–en_GB
Instagram Slider Version :1.4.3
Theme Name : Themify Ultra
My Problem : This message appears above the slider, which is bottom left on the Homepage.
Warning: Illegal string offset ‘standard’ in /var/sites/c/clentparishcouncil.gov.uk/public_html/wp-content/plugins/instagram-slider-widget/instaram_slider.php on line 624

Thank you

https://wordpress.org/plugins/instagram-slider-widget/

The page I need help with: [log in to see the link]