Zucca seems like a very sweet pup and we would love to see some video of her doing what she loves most. This will allow us to compare the session from your video post to how she presents when she is over the moon with joy. Could you post a short video (less than 1 minute) of her doing her favorite activity with you?
She is presenting stress signals and is demotivated in this video. Could be the basement itself or the challenge was too much. Seeing her joyful side will help us to better understand how much of what we are observing is stress.
You are right not to use a leash if she has a negative associating with it. Everything about truffle hunting should be fun.
What are her favorite treats? What are you using for training? Does she like toys?