Unit `pulseaudio.socket` not found

For about two months now, pulseaudio won’t start anymore.
My only audio-related configuration at the moment is hardware.pulseaudio.enable = true and that’s it.

Since pulseaudio is a user service now, I would expect to be able to start it like systemctl --user start pulseaudio.service.
However, systemctl just complains about being unable to find the socket file.

The weird thing is that there is a socket file:

da@merkur ~ [4]> systemctl start --user pulseaudio.service
Failed to start pulseaudio.service: Unit pulseaudio.socket not found.
da@merkur ~ [5]> systemctl status --user pulseaudio.service
● pulseaudio.service - Sound Service
     Loaded: loaded (/nix/store/sv8rzg5lfslk0wd2r7licb5cfxwdm0ck-pulseaudio-13.0/lib/systemd/user/pulseaudio.service; indirect; vendor preset: enabled)
    Drop-In: /nix/store/m2f6j23jdrf661hq594mdng5hhl9abx4-user-units/pulseaudio.service.d
     Active: inactive (dead)
da@merkur ~ [3]> systemctl cat --user pulseaudio.socket
No files found for pulseaudio.socket.
da@merkur ~ [1]> ls /nix/store/m2f6j23jdrf661hq594mdng5hhl9abx4-user-units/pulseaudio.*
/nix/store/m2f6j23jdrf661hq594mdng5hhl9abx4-user-units/pulseaudio.service  /nix/store/m2f6j23jdrf661hq594mdng5hhl9abx4-user-units/pulseaudio.socket



This may or may not be related to Pulseaudio not started after upgrade to 20.03