Comment # 5 on bug 953954 from Wolfgang Bauer

(In reply to Charles-David Hebert from comment #4)
> 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...).

Yes, likely.

> 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.

The workaround is to toggle one of the categories on the "General" page, or
disable some plasmoid (preferably the affected one, I'm not sure ATM if others
would have any effect) and then enable it again (press at least "Apply"
inbetween).

Toggling the "Hidden"/"Shown" state in "Entries" does *not* help.