Every Time a Metal Vulkano errupts for the first time and a metal tile is formed, it stops transfering heat until reloading.
In this case it stays at about 1000°C even with a tempshiftplate behind it and in fluid uranium as heat-transfer-medium.
When I reload the game the metal tile transfers its heat and it quickly transfers heat again.
So if you load the game you will see the fast heat transfer. It does not happen without reloading and it stays at ~1000°C
EDIT: Same happens with the other Vulcano on the right... almost directly after loading the savegame!!!
EDIT2: After some cycles... the other vulcano broke out again. I did not transfer any material. It stays at ~1000°C and does not transfer heat. :
When I reload it transfers heat again like it should.
Look at description. Savefile attached.