I’ve been putting up with this for years, but it’s just getting to be too much trouble. I’m on 6.0.1. If I select a page, and select the Code Editor, and make a trivial change, it can modify the HTML, and make the page useless. And it’s not recoverable unless you can remember exactly what you wrote before, or you go back to a backup database.

On the current page I’m editing, a trivial text change deletes all the hand-coded span tags on the page, and changes all occurences of <li><a id="foo">text</a></li> to <li><a id="foo"></a>text</li>; this has lost all the links and changed the colours.

I’m on Gutenberg at the moment. I’ve tried to fix this historically (pre-WP6) by installing the Classic editor, but it made no difference.

Any ideas? Thanks.