Wordpress - Page 404

I have newly installed h5p plugin on existing webpage. When I add h5p content (360 virtual tour) to a page (via a shortcode), entire page becomes unavailable: I get a 404 page not found error (within wordpress).

When I disable the plugin, the page works again (with shortcode writen where the content should be if plugin was available).

Any thoughts?

Using WordPress 5.8.1(Guttenberg)

with a custom child theme, based on Genesis Framework 3.3.5.