If XDG_RUNTIME_DIR is unset mpd, pavucontrol and most certainly everything using pulse fails to connect to the server. This is the case if mpd is started via the systemd unit file. Even if it is configured to be run under my user. Reproduce: unset XDG_RUNTIME_DIR; pavucontrol This is probably related to #57280.
Turns out this is mostly intended behavior as XDG_RUNTIME_DIR is bound to user sessions and won't survive a full logout.
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