External Links in Custom HTML Blocks

On a new page I create a “Custom HTML” block. If that code contains links that point outside of the website I cannot publish or update and get an error that says something about incorrect JSON response.

Seeing as I can have external links work in other types of blocks -for example paragraphs – my question is: is this a bug, or is it a feature? Or is it a setting I can change somewhere?

This is on up-to-date (as of yesterday) WordPress and Twenty Twentytwo.

Thanks for reading. Appreciate any pointers or ideas as to how to solve this.