This has been said before but there is just a huge amount of misinformation about the blue led indication on the Sunhan amps.
The Sunhans boost in both directions, transmitting and receiving, but can only operate in one direction at a time.
The booster looks at the signal strength on the RADIO port to determine if it should be in receive mode (WHITE LED) or transmit mode (BLUE LED).
If the signal level is above a certain threshold it switches to transmit mode.
ONLY ONE SIDE of the RC transmits. You can't assume that it's the left side or the right side since it depends on how the cables were routed when the antenna mod was done.
It is NOT abnormal for the booster that is on the receive-only port of the RC not to show blue because this booster should NEVER go into transmit mode.
I suspect that when you have 2 boosters very close together, and 2 antennas very close together, and close to the RC, especially if both boosters are operating from a common power supply, that it's certainly possible that enough RF energy leaks from the transmit side booster when it is in transmit mode to cause the other booster to go into transmit mode periodically as well.
This should not cause any problems if it happens. But, the presence of 2 blue LEds doesn't mean it's 'right' and having only one blue LED isn't 'wrong'.