From -9.15pp to +0.61pp: An engineering journey through four DPO iteration failures

An engineering team conducted four DPO training iterations on Qwen2.5-Coder-7B-Instruct, aiming to surpass its 87.20% HumanEval pass@1 score. The initial three attempts failed due to pipeline bugs that were not caught by existing quality gates, with the fourth iteration ultimately yielding a +0.61pp improvement.