I have a volcano tamer that relies on conveyor rail thermal sensors to shut of a conveyor chute. I have noticed that the rail with the sensor sometimes remains empty even though it should allow items to pass over to it. My fix was adding a second sensor with a filter gate, however i noticed the same issue with the other sensor, although less frequent.
I have a feeling this has something to do with load sizes on the conveyor rails.
Here is my volcano tamer:
The way i encountered the bug is to have a thermal conveyor sensor controlling a conveyor chute.