Excel & Sheets Optimization Expert Needed

I have a large, formula-heavy file that lives in both Excel and Google Sheets. Over time it has become sluggish, occasionally throws #REF! and #VALUE! errors, and the user-facing buttons or links sometimes stop responding. I need the workbook streamlined so it recalculates quickly and returns the correct results without breaking its current dashboards and pivots. Your task is to trace the slowdowns, repair or rewrite the problematic formulas, clean up unused ranges and hidden sheets, and generally make the file faster and easier to maintain. That may include replacing volatile functions, restructuring long chains of VLOOKUPs, QUERY or IMPORTRANGE calls, and tidying conditional formatting that’s weighing the file down. If a bit of Google Apps Script or VBA is the cleaner solution, feel free to incorporate it—just document any code you add. Deliverables • Optimised workbook with all existing functionality preserved • Corrected, efficient formulas with no visible errors • Brief in-sheet notes or a separate changelog explaining what was changed and why • A short set of recommendations so I can keep performance high moving forward Acceptance criteria • No #REF!, #N/A, or #VALUE! errors in normal use • File opens and recalculates within an agreed-upon benchmark time • Existing dashboards, pivot tables, and interactive elements continue working exactly as before If advanced Excel functions, Google Sheets, and performance tuning are second nature to you, this should be a straightforward yet satisfying project. Let me know how you would approach the cleanup and share a sample of similar optimisation work you’ve completed.