Could this plug in be creating image errors?

I only have this plug in active on my site but I’m getting image errors in my slider (the image doesn’t display and distorts the size of the slider). I’ve contacted the theme provider but they tell me to disable my plugins. The odd thing is that it doesn’t happen every time so it’s very difficult to determine if it’s this plugin that is causing the error (I hope not coz I love it!).

Can anyone suggest a fix please?

https://courtyardarts.org.uk/testwp/wordpress/

https://www.ads-software.com/extend/plugins/ajax-event-calendar/