Sorry to hear that, but academically very interesting.

Did you try to recover the traffic? If yes, what did you try and did it work?

Also, after setting the permanent redirect, I believe it would be a good idea to update the internal navigation of the site so that all links are formed with https. That way, both the crawlers and the web server will have less work to do and eventually, the entire site will be indexed/updated in the search engines with the https protocol.