I appreciate the suggestion, but this does not appear to be my issue at first glance. I am editing as an Administrator and I do not think I have Multisite enabled (though, to be honest, I do not know how to tell for certain). Moreover, the HTML I get is different from the “similar situation” link you provided. When I paste the content from that issue:
<!-- wp:paragraph -->
<p>before</p>
<!-- /wp:paragraph -->
<!-- wp:html -->
<script>document.write('<div>hello world</div>');</script>
<!-- /wp:html -->
<!-- wp:paragraph -->
<p>after</p>
<!-- /wp:paragraph -->
I get even less:
<p>before after</p>