First of all welcome to the forum
1. Bedding
Someone already said that but Aspen is a real humidity killer and unless you live an a very humid area, that's something you want to avoid. Cypress mulch and these Coco chips are the best way to go. They maintain lots of humidity and it's just easier. With Aspen you'd have to spray way more.
2. UTH
I really don't know lots about UTH, so I don't know the answer to your question. Maybe you should try to measure the temperature at different points of the UTH. It sounded like you just touched it and determined whether it was colder or warmer. Depending on your body and surroundings these examination can be faulty.
3. Other mistakes
Three things come to my mind.
- Even if it's your first snake, quarantine it. You don't have to do the regular three months if you don't have any other reptiles but I'd do at least about 2 months. Look for mites and examine the ball python's behaviour closely. I know people here don't agree with this but maybe even do a fecal.
- Don't handle the snake until it has eaten at least three meals in a row. Make sure to feed whatever the breeder was feeding. Start feeding about a week after the snake arrives.
- The last thing was a mistake I made myself. Keep your enclosure secure! If it's not secure, the snake will escape. On the first night I had mine, I found him in some newspaper pages right next to his quarantine box.