The web server has been unstable for the last week or so. This issue was traced to a combination of using Apache 2.2 and a needlessly complicated certbot setup. The latter would lead to apache2 shutting down seemingly at random whenever certain certificates were updated. For anyone else that has this problem and stumbling on this post, the solution is to edit the [renewalparams] section in /etc/letsencrypt/renewal/*.conf so that it looks something like this:

# Options used in the renewal process
[renewalparams]
account = xxx
authenticator = apache
installer = apache
server = xxx

The important bit is that authenticator and installer are both set to apache and that there are no hooks in there that mess with the apache2 service.

I have also set up Nock Nock on my phone to notify me if somehow the website goes down again.

Hidden service changed to v3

The Tor hidden service has changed address from xynphzf7j7newda6.onion to pfcgmo5hwfffwhis3zty2u2ufryrnzypue34h74va6ykw5iazgcvvtqd.onion. This is due to v2 addresses being deprecated and the tor service refusing to advertise them.