Working along the lines of your thinking in regards to Tuesday following the person’s track rather than searching for the scent, you have identified an challenge through GREAT self-analysis Annie.
You have identified a possible shortfall and have tested it by throwing a target into an area where you haven’t walked. Tuesday could find the scent but not the target.
Pavlov is always on your shoulder. We need to be aware of patterns of behaviour that we consistently do without realising until a behaviour appears in our dogs. It could be that you changed the pattern that Tuesday had learned (human scent equals truffle) and needs to learn a new pattern.
What you did with her to help her find the truffles was a good solution to give her a win. Although, that could also be part of the challenge she is having (human = truffle).
Go back a few steps and check her comfort and learning with finding a sample away from you (you mentioned distance in your first video upload) and working on increasing that distance in a ‘simple’ environment with low distractions. Working in an open field/park with areas of short and long grass, throw samples into the short and then long grass for Tuesday to find. Video her and watch her search language. Is Tuesday confused about what is asked? Does she find the scent plume struggles to locate the sample/truffle? Has the search lost its ‘fun’?
You mentioned that you only had a small amount of truffle left. Have you trained with larger quantity than you had today previously? Do you think that any of the sample tins or cloth could have put him or, do you think the samples could have been left to cook for too long for the size of truffle? Were the truffles too old and low in scent?
Sometimes going back to review and redo earlier steps will help both of you in the task you are doing. Keeping a chart of each training session to see if she is improving or plateauing. This can happen in training, and going back to earlier successful approximations and taking your time to move forwards can often cement the outcome from training.
At 2:07 Tuesday appears to be eating, and it could (I don’t know Tuesday that well) have been a stress indicator and the training stopped. Her expressive tail was not working the same as previous, was Tuesday having an ‘off’day.
Look forward to hearing from you.