"not a valid json response" error when saving page with shortcode.

[andysavage]

In WP 5.8 with plug-in v 1.2.2 I get an error "Updating failed. The response is not a valid JSON response." when trying to save a page with the shortcode in. I tried saving other shortcodes, including ones that don't exist, as well as non-shortcode content. Only the [wp-todo] shortcode produced the error.