In the attached save, there is a door at 460C that does transfer only minimal heat to two metal tiles next to it (at 125C, no large heatsink attached to them). The problem persists on save/load but goes away immediately if the door is destroyed and rebuilt with the same material, nicely demonstrating the earlier behavior is broken. The save is centered on the problem door.
I did have the same problem earlier with the same door, but it fixed itself somehow, probably due to save/restore. Not this time.
Watch not much heat get transferred. Tear down door and rebuild with same material, watch a lot of heat suddenly getting transferred as it should