I checked the logs and it seems the main difference from other responses via email is that instead of replying to qubes_os+[some_topic_numbers]@discoursemail.com you sent to qubes_os@discoursemail.com. Quoting from your email headers:
My first guess is you replied somehow differently than usual. Could that be the case? Please double-check the reply to header and see if it it arrived somehow differently on your inbox (compared to other emails from the forum)