[claviola]

Are you using systemd-resolved? If so, it's actually a symlink to /run/systemd/resolve/stub-resolv.conf, and all you need to do to manage it yourself is to turn it into a regular file of your own. This is explained in the admittedly very long commented out text above the actual directives.

[johnisgood]

No, it is a runit-based system. I think the issue was related to resolvconf + package updates overwriting the file.

That said, I am sure your comment will be useful to some!