Paste and re-saving breaks links

On the current EM, 6.6.1

Using the Event Manager form, on settings using the Visual Editor setting, I get the event description field and I take an email and paste it in. It contains a link. This is on a Gutenberg site using the Fork theme.

Something happens when I paste, or when I edit and resave which seems to be a “well known problem”.

The link acquires an ever-growing number of quote marks so breaks on the original paste or when the event is edited with the front end editor. The link text remains so the error is hidden. I can go into the link, take out the quotes and save it, then save the event and it is ok, but if I re-edit the page, the editor breaks the link again.

Also, if I round-robin the editor, I use the excerpt break marker to allow for a sensible excerpt but if I re-save after an edit, on opening instead of the dotted line, it creates a <!—more —> piece of text in place of the hidden code.

It should be easy enough to reproduce.

I’ve tried setting off the visual editor but that looks nasty for my innocent users. From Googling I think it is a well-known problem, and it is not clear to me what I can do to poke my config to stop the underlying WP-Editor breaking my links.