Получил-таки от райзапа письмо о том, в чём было дело и почему мой аккаунт не работал:
Hi, We are very sorry you have been inconvenienced by your account not working. We attempted to contact you a few times in the last several months about the safety of your account because we have been under constant attacks by people attempting to compromise users. We had found that your password was too simple, and an easy target for compromise. We had asked you to change your password to something a little more challenging before March 15th, it did not appear as if your password was ever changed, so we were forced to disable your account so that we can get you to change it. We have re-enabled your account, but you will need to reset your password before you can access it. You can reset your password here: https://user.riseup.net/forms/password_reset/first To change your password you can do so by navigating to riseup's main page, look for the "Email" section where you can find a link to "Change my settings". That will bring you to the correct location to set a new password. If you are concerned you might forget your new password, set a secret question and an alternate email that you can use to gain access to your account if you lose it. If you value radical alternatives to the corporate internet, and you want to see us stay around, then we need your contribution! Our service is paid for entirely by small donations from users like you. Please donate generously at: https://riseup.net/donate
То есть, они закрыли мой аккаунт, чтобы его не взломали. Чем-то напоминает логику охотников из сауспарка — "Давайте убьём всех этих животных, чтобы они не сдохли с голоду!". Занятная политика у чуваков, ничего не скажешь. Ну ладно, аккаунт восстановил, пароль сменил, пока живём.