Senior PHP/MySQL Engineer Needed to Diagnose Data Pipeline Bug (WordPress)

Goal I am not looking for someone to rebuild my application. I need an experienced PHP/MySQL engineer to diagnose a pricing pipeline and identify exactly why portfolio values are incorrect. The deliverable is a diagnosis and recommended fixes—not implementation. About the project PokeSplain is a Pokémon card analytics platform built on: WordPress Custom plugin PHP MySQL Custom REST API JavaScript frontend The application already works. The issue is that many portfolio cards show: $0 values incorrect market prices some cards price correctly while others do not The pricing pipeline already exists. Current pipeline Raw eBay sold listings ↓ Normalizer ↓ normalized_card_id ↓ card_sales ↓ price aggregation ↓ card_prices_current / ps_card_market ↓ Portfolio API ↓ Portfolio UI Somewhere in this chain the data is becoming incorrect. What I need I want someone to trace the complete pricing pipeline and determine exactly where the failure occurs. I do not want guesses. I do not want code rewrites. I want evidence. Deliverables Provide a written report including: Where the pipeline first becomes incorrect Which function(s) are responsible Which SQL queries are incorrect (if any) Any schema issues Any incorrect joins Any incorrect assumptions Whether the bug is: normalization aggregation SQL API portfolio query frontend A prioritized list of fixes Estimated effort for each fix Important Please do not rewrite the application. Do not redesign the database. Do not replace working code. Only identify the root cause(s). Skills Senior PHP WordPress plugin development MySQL SQL optimization REST APIs Debugging legacy systems To apply Please answer: Have you debugged complex PHP/MySQL data pipelines before? How would you isolate a pricing bug like this? What information would you need from me? Final deliverable must include the exact filename, function name, and line range for every issue found, plus a concise explanation of why it is a bug.