My jbl flip 4 suddenly had no sound (no power up sounds either). Charged and paired perfectly but didnt sound. I arrived to this page and tried the different solutions with no luck. Just when I was about to give up I did the following and worked!!
1- Jbl flip turned off.
2- Press power on button but don’t release. Even if light in the button turns on.
3- Keep it pressed til you here the power up sound .
4- Sound is on again!