One more angle to consider is wicking. Handmade jars can sometimes be underwicked for the diameter, which makes them more prone to tunneling in drafty or cool rooms. You can still get a decent recovery though. Trim to a quarter inch and do a long burn in a calm spot. If the sides refuse to melt, the foil collar trick is your friend. If you notice the flame is tiny and struggling even after you do that, reach out to the maker to ask about the wick choice. They might suggest a swap or offer a fix. For prevention, start with a full edge to edge melt on the first burn and keep the wick tidy to maintain a steady flame.
