And just to explain it a different way. All breakers are on.
Turn off microwave breaker, microwave display goes out.
Turn off refrigerator breaker, microwave display goes out and refrigerator 120 volts outlet is dead. Verified because refrigerator switches to gas mode.
And since the refrigerator breaker is tied to both outlets for the refrigerator and the big convection oven/microwave this 15 amp breaker will trip occasionally. Which my guess is if the 300 watt refrigerator heating element happens to be on at the same time the microwave is in use it trips.