I think Efirmovich has the answer.
Oil content reducing, and momentarily the pump fails to maintain oil pressure above the minimum. Caption & Bong are triggered, but as the "dip" below minimum was momentary the light is extinguished and by the time you look down - hence no caption; the system is "reset" to normal conditions. Later, this happens again.
Being myself a coward in the RH seat, my personally imposed rules for flight include "you bong, I land". With a caption, that would be immediately / as soon as possible / and theoretically "as soon as practicable" per the flight manual (though unless it is something I fully understand - I had a generator failure, for example - you will find me in a field - see above) then unless . Without the caption, I opt for "as soon as possible". I figure that working things out / chatting with an engineer on the phone whilst standing next to the machine is my personal risk-limit.