I'm sure this must have been reported already because it happens literally every time you try to use this feature, but it may not be a well known feature.
While spectating, on the map or scoreboard, you can click on player icons or names to switch to spectating that player. But after doing this a few times it causes various issues including black screen and missing sounds such as gunfire and footsteps.
The black screen issue goes away if you hit Esc twice, but the sound issues persist until you respawn.
edit: I suspect the issue may only occur if you switch players just after the first one dies. Since it might have to do with the blackout effect.