If a player has active hoppers/furnaces and tps away from those loaded chunks, when they return (after the chunks unload) the furnaces/hoppers can occasionally freeze.

Furnaces in particular refuse to smelt, regardless of whether you remove fuel/items and reload them. Only solution is to destroy furnace and replace.

This is only happening to a subset of users at this time, so I am struggling to find a common link, hoping to add more data soon.