First of all, I need to point out that I have only played custom games with bots so far.
The bug doesn't happen all the time, but occasionally, the announcer and champion voices glitch out and get disabled in the middle of the game.
The background music, sound effects (including champion sound effects that are not the voices) work fine.
Once the audio bugs out, there is no way to fix it through the sound option settings in the ESC menu.
Resetting to default, muting/un-muting, etc. does not fix anything.
I'm not sure exactly what causes the bug to occur.
I'd say this bug occurs about once out of ten games, give or take.
This bug had occurred in a previous patch several months ago, with the same reproduction rate and all.
It had been fixed, but it seems like it's returning this PBE patch.
**I'd say the only difference this time is that once the bug occurs, *the game freezes several minutes afterwards.***
I have not tried leaving and reentering the game, because that would only cause the actual game to end.