404 error on all pages using shortcode

The above link is only one example of the problem we’re having. Every single page with the shortcode embedded has recently (I think we noticed it in the last 2-3 days) started giving a 404 error instead of embedding the slideshow ??

This could coincide with an upgrade to the most recent version of WordPress (5.3)

For the page above, the shortcode is:

[fshow photosetid=72157700378684122]

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