12.If the left and the right earplugs are disconnected, how to do to get this issue sorted? (single earplug is silent or the blue light flashes continuously and rapidly)

There is no solution for this kind of earplug disconnection. What can be done is to long press each earplug for 10s under off state until the indicator light turns to pink, and then stop pressing, putting two earplugs together. At this time, the pink light will turn into blue that flashes rapidly.

After about 5s, the earplugs will automatically match to each other and enter the pairing mode with the front end (with the red and blue light of the main earplug flashed alternately).

(note: when the earplug's blue indicator light is continuously and rapidly flashing, it means one earplug is entering pairing mode with the other earplug. Press the other earplug for 10s to enter the matching state.)

You could also read this video for help instead: