Bottom half of page disappears in Edit Mode

The lack of a closing tag for an HTML block will cause problems in the edit view. You can obtain an editable view very similar to the revision view using the code editor. Access it through the 3 dot icon at upper right. Simply replace the missing tag where it belongs and save.

I’ve no idea why it would disappear, but the code editor is how you would replace it. As a guess, examine the HTML block’s content carefully. If there are any tags that are not properly balanced or nested, it could cause the editor to do strange things with other tags.

Thanks. In this case, the problem is not yet solved, but I’m sure you are right that I should be able to spot the issue in the code editor, which I was not even aware of.

I suspect there is still an issue with unbalanced tags somewhere, likely in your custom HTML content.

Try evaluating the page through a HTML validator like this one: https://validator.w3.org/

Use the options to validate as document type HTML5. You may get errors of little consequence. Look specifically for tag not open or tag not closed errors.

You were right about the missing tag. This was missing: <!– /wp:html –>, and everything on the page after that point disappeared. In Code Editor Mode I could see that it was missing, but I was not able to insert it and make it work. So I copied and pasted the page into Notepad++, and then added the missing tag. Now it appears to be working fine.
Thank you for your advice and your follow-up!

That’s strange you couldn’t use the code editor. It’s sort of the whole point of that view. Clever work around though, nicely done! Glad it’s all sorted.