Just tested the game, got two ghosts that have freezing temperature and it's working as it should be. Do you have latest version? I remember that map being bugged in previous ones.
No, before Kupper even appeared, I had already placed two candles right next to her spawn point. The candles didn’t go out during the ghost hunt. I remember that in the previous version, candles would go out during a hunt.The conditions were just right for placing incense in the ghost room at that time.At that time, I hadn't used incense in the ghost room yet. I thought it might have been a bug, so I quit the game.
I tested it multiple time using an exported project. It's working as it should be. Just in case there's any bug that happens when candle is turned off automatically I checked hiding, getting caught and switching items. But nothing is causing any issue. If you know anything specific thing you did before trying catching the kupper let me know.
"I wasn't doing anything special. At the time, I was looking for evidence of a ghost and saw a puddle of water on the floor. I knew it was a Kupper. The ghost room was in Luna's room, and the spawn point was between the bed and the dressing table. My assistant was Tess, so I had her take a candle. I used a thermometer to find the ghost's spawn point, then dropped the thermometer right there. Just then, a hunt started. My assistant dropped her candle, but it was still burning. I was within ten meters of her. I also had another candle in my hand. When the ghost spawned, before it even started moving, I waited for a while but nothing happened, so I hid. After the hunt, the candle my assistant had dropped was still burning. Then I took the other lit candle from my hand and also placed it on the floor. When the ghost hunted again, it still didn't knock down the Kupper, so I hid once more. After that, no matter what, those two candles couldn't knock down the Kupper."