The issues have now been resolved.
The issues surrounding voice chat should now be resolved. Drop in and chat with your squad!
— Fortnite (@FortniteGame) September 16, 2018
In an updated posted on /r/FortniteBR, Epic Games has addressed an issue with degraded voice chat in Fortnite.
Not all players will experience issues, but if you are be sure to provide your details in the comments of the Reddit post. We’ll update once Epic has resolved the issue, as of an hour ago it is still being investigated.