My brand new JBL Flip 5 seems to have an issue with the buttons: they don't work as expected.
Serial number: GG..55-LL02...54
Funny enough, most of the hidden (for the average user undocumented) functions don't work either.
Luckily resetting the device by pressing play(phone) and volume + buttons together works, which allows the speaker to connect to a new device.
From the Flip 5 Service Manual:
BOTTON FUCTION MAPPING
Button Pattern | Action | Indicator
Volume + & Bluetooth | Long press 10s | Enter HID DFU mode in On Mode.
Volume + & Phone | Long press 2s | Reset to factory default in On Mode.
Volume - & Bluetooth | Long press 10s | Enter by-pass mode in On Mode.
Volume - & Phone | Long press 10s | Enter Regular DFU mode in On Mode.
Volume - & Link | Long press 2s | Show SW version in On Mode.
Volume + & Link | Long press 10s | Enter Demo mode in On Mode