Contact Form 7 Mail template will not update

Good day to you.

I’m trying to make a number of changes to an existing, and operating, copy of a Mail template driven be a new, and operating, contact form. The existing Mail template works to the extent that its Tags line up with those on the form.
The problem is that I cannot make even the simplest changes to the Mail template, not even move a line. When I click Save, there’s no success popup nor other sign of success.

This is on Theme The7 using WP 5.9.1 and Contact 5.5.3

Thank you!