Hide My Email has gone rogue - takes over responses

I have never deliberately used Hide My Email. But it now decides fairly regularly that I want to hide my email when I reply to messages. Switching to my regular email in the scroll box doesn't work. It switches itself back. Happily it doesn't actually ever send the emails (since I want my emails to have my actual address). It gets confused by the server it is supposed to use. Then it flashes an error message that says something like update your forwarding address. This repeats as many times as I try.

The only way I can actually send the email is by deleting it, quitting Mail, restarting Mail, and then drafting the response again.

I have tried completely deleting the generated random email addresses, but that doesn't help. There is apparently no way to just turn Hide My Email off, unless I have missed it.