Basically when using anything that requires fuel to create materials, they stop burning. So i will leave a furnace on to cook metal over night and then the next morning i will go on and the furnace has turned itself off. Happens when also leaving it alone and coming back after exploring. Happens with furnace and firebowl cauldron.
Gotta say I have not seen this issue at all, are you playing online or in single player mode? I leave my furnace going overnight all the time and when I get on the next day it’s fine (everything cooked and furnace is now off after having finished). Not sure about cauldron I know I have left it burning when out and about with no problems and probably overnight but can’t specifically remember any instances of doing so.
Maybe a clan mate is turning it off? Or do you happen to get off right before server reset every day? I don’t think reset would turn it off either but it’s possible.