Comment # 4 on bug 953954 from Charles-David Hebert

In answer to(In reply to Wolfgang Bauer from comment #3)

It is probably related to the same Bug that you pointed at bug.kde.org
It is reproducible and many systems and with many distros using plasma 5
(Manjaro, Leap, fedora...).

For my part, the volume icon always disappears after a reboot, leaving an empty
space. Also, toggling the "Auto" to "Shown" Button in the "Entries" in the
system tray settings does not solve the problem.