I am using volume keys. All seems to work, but often applications loose sync with master volume, having own value and don't follow master anymore. I click volume icon, applications tab and set slider to 100% manually for all apps. So in general it working well, but after some time (1-2h of volume changing) it stops moving application sliders, and volume is low on 'maximum'. Sometimes volumes differ for every application. I have this bug since Plasma 5.8.2 Plasma 5.9.4, Gentoo-hardened, kde-overlay unmasked, Linux-4.9.15 + Grsecurity (with paxctld and exceptions for most kde core).
You can try disabling flat-volumes (really annoying feature that is being disabled by default in almost all distributions) in pulseaudio settings. Volume keys only changes only volume of audio device, not applications.
When I change volume with keys or mouse scroll on the icon, volumes changes on all playback streams and master. If I change volume and click the icon, I see same levels on applications and analog output. And sometimes sync looses, application volumes stop following 'analog output' until you max them to 100%
> When I change volume with keys or mouse scroll on the icon, volumes changes on all playback streams and master. That's pulseaudio's flat-volumes feature. If it gets out of sync after some time, it's bug in pulseaudio and you should report it there.
Thanks for information. I use pulseaudio 10. I'll try disabling this feature and will report them.