Couldn’t find it on your lovely website to see what is wrong.
If you can recreate the page with the shortcode or block and post the url here I can see what is wrong for you.
Or if you right click on the page and then inspect, you will see any errors in red – copy and paste them and it will give the clues!
I can’t see anything in red within the code. On the “Console view” there’s one error: it says, “Unchecked runtime.lastError: The message port closed before a response was received.” Does this help diagnosis?
The url is https://hunsdonchurch.org/sermons/
It makes no difference whether the player is created with the shortcode or the Gutenberg block.
Thanks for looking at it for me.