This is fixed ONLY when using the new audio mixer in 4.15
Game sounds can no longer be heard after unplugging and re-plugging back in a USB headset during a match. This also occurs when plugging a USB headset anytime during the course of the match.
1.Plug in a USB headset.
2. Launch client in the latest cooked build
3. Get into match with any hero.
4. After load in unplug USB headset.
5. Plug in USB headset
RESULT:
Game can no longer be heard.
FREQUENCY:
3/3
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-26051 in the post.