I've done some research (as far as I can do) into this bug, @EA_Ataashi
I got 4 videos of this bug happening, but I've had it more than 4 times for sure. I just didn't record everything.
The videos are posted below. Maybe on your side, you could find additional information based on the facts that are stated below. I hope you can proceed to check what happened in these matches around that time. (I've specifically noted down the time and information to find that match).
VIDEO-1
15 April 2018, 18:29:25, GA NABOO, DROIDS, EUROPE, PC
Me playing as bossk, other team has Lando and Yoda. 2nd phase.
Sound was lost: Exactly at the moment Lando was defeated. (1 opponent hero/villain that doesn't belong to era of Naboo)
VIDEO-2
15 April 2018, 19:15:28, GA KASHYYYK, REPUBLIC, EUROPE, PC
Me playing as Rey.
Sound was lost: Exactly after the animation of Reys mindtrick was finished and I started with her rush. (Hero that doesn't belong to era of Kahyyyk)
VIDEO-3
23 December 2017, 17:03:50, GA, KASHYYYK, REPUBLIC, EUROPE, PC
Me playing as Leia, second phase.
My sound was not lost, but someone in the chat noted that it happened to him. Giving this footage and data with the hope you can use it.
VIDEO-4
08 April 2018, 22:40:14, GA, KASHYYK, DROIDS, EUROPE, PC
Me playing as a droid, second phase again.
Sound was lost: Exactly after Rey hit me with her forward punch (Hero that doesn't belong to era of Kashyyyk).
Seems like I found another one, one more recent.
VIDEO-5 (seperate)
16 May 2018, 19:27:23, GA, NABOO, DROIDS, EUROPE, PC
Playing as the jumptrooper class of the CIS.
Sound was lost: After Vader died (Hero that doesn't belong to era of Naboo).
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CONCLUSIONS
It is limited to Clone Wars era maps It actually happens on some other maps as well. Death Star 2 springs to mind. However, the highest probability is on the Clone era maps.
It is also worth noting that it only happens in GA (as far as I know).
It probably has something to do with heroes/villains, possible from ones that don't belong to that era.
It can happen to any class.
Actually, it makes SENSE that it only happens in the second or third phases since mostly then HEROES are being used.
EDIT: Posted a mistake. Not only on Clone Wars era maps, but also on certain other maps.