How Four Hidden Bugs Were Draining a Tool's 8,000-Daily-Job Conversion Rate

A developer running a small audio conversion tool processing roughly 8,000 jobs per day documented five months of debugging that pushed its completion rate from around 92% to 99%. The tool, built on Flask, Redis, RQ workers, yt-dlp, and rotating proxies, suffered from four bugs that only surfaced under real production load. Key issues included two proxy entries that shared an upstream gateway and were mistakenly treated as independent, a slow proxy-rotation call blocking the request path and inflating p95 latency, and a fallback mechanism that ignored disabled proxies and routed traffic to consistently failing ones. The fourth and most impactful fix involved detecting permanent errors — such as deleted videos — early, cutting wasted retry attempts on roughly 2% of all jobs and freeing up capacity for other users.