I don't know how but sometimes when I mess up my smelting area the furnaces try to switch to steel production and after I fix all this happens:
I did not test this in the latest release.
It happens when the iron ore runs out and the furnace try to feed iron plates becaus I have the resources on one belt. After I fixed the iron supply and cleaned all steel plates some furnaces are always stuck. i don't know if this is related to that but I noticed that chemical plants sometimes don't update the fluid input slot or not even accept fluid at all.
Save: https://www.dropbox.com/s/8r495s131l7oj ... e.zip?dl=0
Ok, thank you for the report, I was able to find out what is wrong. It had nothing to do with mods actually, and it was related to wrong details of internal furnace logic.
It is fixed for 0.12.13 now. There is also automated test covering this.