
In this image all trains are not moving. The circuit train is blocking the copper plate train.
Pausing the circuit train removes the yellow light and frees the copper plate train.
I have seen this problem 5 times on my world with over 100 hours.
I have tried reverting to an auto-save to deterministically watch it re-occur, but have so far been unsuccessful.
My gut feeling says it occurs more when a slow train gets in front of a fast train (slow copper getting in front of fast circuit).