I just upgraded (in-place) my Linux OS (from openSuSE 15.1 to 15.2). After the upgrade, the system tray icons for audio/sound and kmix (the "loudspeaker" icons, see https://www.cleanpng.com/png-loudspeaker-computer-icons-sound-icon-call-icon-1173288/ have a circle-backslash (see https://upload.wikimedia.org/wikipedia/commons/thumb/3/31/ProhibitionSign2.svg/150px-ProhibitionSign2.svg.png) in place of the projecting sound waves.

Based on my initial use, the sound appears to be working properly as before the upgrade.

Why are the circle-backslash symbols present? Is this an ffmpeg codec permissions issue?

More likely either an icon issue (depending on your overall Plasma Theme and Icon theme), or you have several channels of which one is muted.

Thank you for the reply. Please note that I did an in-place upgrade and didn't change anything in the configuration - the circle-backslash symbols were not present prior to the upgrade. The KDE desktop settings dialogue for audio does not yield any clues.

Again - the audio works; to my knowledge, no expected audio is missing.

Maybe ask your distribution, then? If you didn't change anything in your configuration then one of the updates must have triggered the problem.