Description of problem: On both KDE Plasma 5.11 (F27+snd_hda_intel) and 5.10 (F26+snd-virtuoso) I have noticed that if you close your session by logging out, and you log in again, there is a very high probability that Pulseaudio will not detect any playback device, triggering Volume tray icon to "mute"
https://fedoraproject.org/wiki/Common_F27_bugs#Pulseaudio_fails_to_start_if_user_logs_out_and_back_in_again_very_quickly includes some workarounds *** This bug has been marked as a duplicate of bug 1510301 ***