CROSS ORIGIN!! Error Cannot Access File

I am trying to test this plugin to display a programme pdf on 3 pages on my website and using the same shortcode.. I have added the link using the button to select the file from my Media library.

I am finding that intermittently I am getting this error – CROSS ORIGIN!! Error Cannot Access File, I cannot find a common cause. Sometimes it works on all pages, sometimes it fails on some, sometimes it works on none. I tried different browsers and I also tried clearing my cache.

Can you help at all to tell me what is going wrong and I can fix it? The following pages is where the pdf is displayed:

https://www.britspa.co.uk/annual-scientific-meeting-2026/

https://www.britspa.co.uk/annual-scientific-meeting/

https://www.britspa.co.uk/event/2026-britspa-annual-scientific-meeting/

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