Tried calling dataset.labels_frame.iloc[0, 0] (where dataset was replaced with my training dataset), and it works fine (I also called dataset.labels_frame.iloc[0, 1] which is shown):

Here’s a small subset of the training data CSV: https://ufile.io/v5elq 1
This is a pretty perplexing issue, because if I just take my custom sampler out of the equation, the DataLoader seems to work fine.