Chosen Solution
I have the JBL Flip 4 for 14 months, it worked fine. However now with the unit turned on, there was no sound or the sound disappeared after a short time (seconds to minutes). All buttons and connections worked. The problem was observed with the speaker connected by cable to the laptop or via Bluetooth to the smartphone. Resetting the speaker (pressing simultaneously play and plus buttons) did not help.
If your JBL Flip 4 speaker refuses to connect to another device through Bluetooth, see the JBL Flip 4 Won’t Connect Through Bluetooth problem page for possible causes and solutions. I searched for many hours on the web and could not find any answer. Finally, by trying various combinations I found that with the JBL FLIP 4 turned on and by pressing simultaneously the Bluetooth discovery mode button (left) and the volume down button the problem was solved.
