The addition of Plasma 5.4 introduced plasma5-pa as the new audio control.
However, the KDE patterns install kmix (what was kmix5).

So, on initial bootup, there is two volume control applets in the systray. And
since they are both listed as something similar in the tooltip, it is hard to
distinguish them (only by looks).

If you go to remove kmix, it wasn't to deinstall several patterns.

Solution: one or the other should now be removed from the default patterns. I
assume that since plasma5-pa is the new one, it should be left and kmix should
be removed from the pattern. I assume kmix should stay in the repos, as not
everyone uses PulseAudio for the new applet to work correctly.