Thanks to
@Pacifico and
@nicole.hopkins for letting me know that sometimes people get added to group message threads in the private message / inbox feature of the discussion forums, can't leave, and are destined to receive every message posted to that group in the future!
Sorry if that's been causing you problems! We put in some changes so that you can edit opt out and remove yourself from group messaging threads. Just go to the message thread you want to leave and tap on the big blue button on the left labeled "Remove from thread". I hope this helps!