If I play with friends Fortnite sometimes without sound the sound goes away from the game that means I do not hear any shots or anything like that anymore but I can still hear my friends talking and answering and plugging in again does not help either
I also had the problem sometimes.
I heard my footsteps and my friends but no shots or anything else.
Activate the sound effect setting to visualize the sound effect.
So you are always safe even if it does not look good.
On which platform do you play? At Playstation 4, this is currently a pre-existing bug that will only be fixed once the round has ended. If you play on the PC, it is probably because of your soundcard or the jack connection has a way. I would rather tap on the latter as you hear the voices.