Blocks overlapping others in page editor

I’ve a strange issue which has appeared. I’ve a page with a group at the bottom of it, but that group is being displayed over the top of content further up. Also, it appears that the content is being displayed *underneath* the panels at the bottom of the page, for example, if Yoast is activated, the Yoast panel blocks part of the editor.

I’ve disabled all plugins and reverted to Twenty Twenty One and I’m still seeing hte same issue.

See https://imgur.com/a/1NhkyCI which shows the block above content in the editor and where it should be in the navigator.

This content displays fine on the page. It’s only wrong in the editor!

Using: 0 plugins. Twenty Twenty One. WordPress 5.7.2.