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My AI model training got stuck for 3 days because of a tiny data format bug

I was fine-tuning a text generator on a custom dataset of forum posts, expecting it to take maybe 12 hours. The training started, but the loss value just wouldn't go down at all. I spent a full day checking my hyperparameters and model architecture before I found it. The issue was a single line in my data cleaning script that was stripping all punctuation, which totally messed up the tokenizer's understanding of sentence flow. Fixing that one line and restarting the training took 10 minutes, but the whole debugging process wasted 72 hours. Has anyone else had a training job get wrecked by something that seemed minor in the data prep stage?
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3 Comments
haydenbutler
Three days stuck on a punctuation bug... that's brutal. I can't believe stripping periods and commas could completely freeze the loss like that. It makes sense though, the model must have had no clue where sentences ended.
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jade226
jade2263d agoProlific Poster
Omg hayden the punctuation thing is so real. @rivera.simon your HTML tag story gives me flashbacks lol. I had a similar issue where my tokenizer was splitting on spaces but not handling newlines, so the model would just jam everything together. What finally worked was adding a custom token for line breaks and padding all sequences to a fixed length so the model could actually see where one thought ended and the next started. Took me way too long to figure that out.
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rivera.simon
Remember that time I accidentally left HTML tags in my training data... the model kept generating broken sentences with
tags everywhere. Took me a week to realize the scraper wasn't cleaning properly.
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